conclusion of literature review essay

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

Literature Reviews

What this handout is about.

This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.

Introduction

OK. You’ve got to write a literature review. You dust off a novel and a book of poetry, settle down in your chair, and get ready to issue a “thumbs up” or “thumbs down” as you leaf through the pages. “Literature review” done. Right?

Wrong! The “literature” of a literature review refers to any collection of materials on a topic, not necessarily the great literary texts of the world. “Literature” could be anything from a set of government pamphlets on British colonial methods in Africa to scholarly articles on the treatment of a torn ACL. And a review does not necessarily mean that your reader wants you to give your personal opinion on whether or not you liked these sources.

What is a literature review, then?

A literature review discusses published information in a particular subject area, and sometimes information in a particular subject area within a certain time period.

A literature review can be just a simple summary of the sources, but it usually has an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

The main focus of an academic research paper is to develop a new argument, and a research paper is likely to contain a literature review as one of its parts. In a research paper, you use the literature as a foundation and as support for a new insight that you contribute. The focus of a literature review, however, is to summarize and synthesize the arguments and ideas of others without adding new contributions.

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone. For professionals, they are useful reports that keep them up to date with what is current in the field. For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper’s investigation. Comprehensive knowledge of the literature of the field is essential to most research papers.

Who writes these things, anyway?

Literature reviews are written occasionally in the humanities, but mostly in the sciences and social sciences; in experiment and lab reports, they constitute a section of the paper. Sometimes a literature review is written as a paper in itself.

Let’s get to it! What should I do before writing the literature review?

If your assignment is not very specific, seek clarification from your instructor:

• Roughly how many sources should you include?
• What types of sources (books, journal articles, websites)?
• Should you summarize, synthesize, or critique your sources by discussing a common theme or issue?
• Should you evaluate your sources?
• Should you provide subheadings and other background information, such as definitions and/or a history?

Find models

Look for other literature reviews in your area of interest or in the discipline and read them to get a sense of the types of themes you might want to look for in your own research or ways to organize your final review. You can simply put the word “review” in your search engine along with your other topic terms to find articles of this type on the Internet or in an electronic database. The bibliography or reference section of sources you’ve already read are also excellent entry points into your own research.

Narrow your topic

There are hundreds or even thousands of articles and books on most areas of study. The narrower your topic, the easier it will be to limit the number of sources you need to read in order to get a good survey of the material. Your instructor will probably not expect you to read everything that’s out there on the topic, but you’ll make your job easier if you first limit your scope.

Keep in mind that UNC Libraries have research guides and to databases relevant to many fields of study. You can reach out to the subject librarian for a consultation: https://library.unc.edu/support/consultations/ .

And don’t forget to tap into your professor’s (or other professors’) knowledge in the field. Ask your professor questions such as: “If you had to read only one book from the 90’s on topic X, what would it be?” Questions such as this help you to find and determine quickly the most seminal pieces in the field.

Consider whether your sources are current

Some disciplines require that you use information that is as current as possible. In the sciences, for instance, treatments for medical problems are constantly changing according to the latest studies. Information even two years old could be obsolete. However, if you are writing a review in the humanities, history, or social sciences, a survey of the history of the literature may be what is needed, because what is important is how perspectives have changed through the years or within a certain time period. Try sorting through some other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to consider what is currently of interest to scholars in this field and what is not.

Strategies for writing the literature review

Find a focus.

A literature review, like a term paper, is usually organized around ideas, not the sources themselves as an annotated bibliography would be organized. This means that you will not just simply list your sources and go into detail about each one of them, one at a time. No. As you read widely but selectively in your topic area, consider instead what themes or issues connect your sources together. Do they present one or different solutions? Is there an aspect of the field that is missing? How well do they present the material and do they portray it according to an appropriate theory? Do they reveal a trend in the field? A raging debate? Pick one of these themes to focus the organization of your review.

Convey it to your reader

A literature review may not have a traditional thesis statement (one that makes an argument), but you do need to tell readers what to expect. Try writing a simple statement that lets the reader know what is your main organizing principle. Here are a couple of examples:

The current trend in treatment for congestive heart failure combines surgery and medicine. More and more cultural studies scholars are accepting popular media as a subject worthy of academic consideration.

Consider organization

You’ve got a focus, and you’ve stated it clearly and directly. Now what is the most effective way of presenting the information? What are the most important topics, subtopics, etc., that your review needs to include? And in what order should you present them? Develop an organization for your review at both a global and local level:

First, cover the basic categories

Just like most academic papers, literature reviews also must contain at least three basic elements: an introduction or background information section; the body of the review containing the discussion of sources; and, finally, a conclusion and/or recommendations section to end the paper. The following provides a brief description of the content of each:

• Introduction: Gives a quick idea of the topic of the literature review, such as the central theme or organizational pattern.
• Body: Contains your discussion of sources and is organized either chronologically, thematically, or methodologically (see below for more information on each).
• Conclusions/Recommendations: Discuss what you have drawn from reviewing literature so far. Where might the discussion proceed?

Organizing the body

Once you have the basic categories in place, then you must consider how you will present the sources themselves within the body of your paper. Create an organizational method to focus this section even further.

To help you come up with an overall organizational framework for your review, consider the following scenario:

You’ve decided to focus your literature review on materials dealing with sperm whales. This is because you’ve just finished reading Moby Dick, and you wonder if that whale’s portrayal is really real. You start with some articles about the physiology of sperm whales in biology journals written in the 1980’s. But these articles refer to some British biological studies performed on whales in the early 18th century. So you check those out. Then you look up a book written in 1968 with information on how sperm whales have been portrayed in other forms of art, such as in Alaskan poetry, in French painting, or on whale bone, as the whale hunters in the late 19th century used to do. This makes you wonder about American whaling methods during the time portrayed in Moby Dick, so you find some academic articles published in the last five years on how accurately Herman Melville portrayed the whaling scene in his novel.

Now consider some typical ways of organizing the sources into a review:

• Chronological: If your review follows the chronological method, you could write about the materials above according to when they were published. For instance, first you would talk about the British biological studies of the 18th century, then about Moby Dick, published in 1851, then the book on sperm whales in other art (1968), and finally the biology articles (1980s) and the recent articles on American whaling of the 19th century. But there is relatively no continuity among subjects here. And notice that even though the sources on sperm whales in other art and on American whaling are written recently, they are about other subjects/objects that were created much earlier. Thus, the review loses its chronological focus.
• By publication: Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on biological studies of sperm whales if the progression revealed a change in dissection practices of the researchers who wrote and/or conducted the studies.
• By trend: A better way to organize the above sources chronologically is to examine the sources under another trend, such as the history of whaling. Then your review would have subsections according to eras within this period. For instance, the review might examine whaling from pre-1600-1699, 1700-1799, and 1800-1899. Under this method, you would combine the recent studies on American whaling in the 19th century with Moby Dick itself in the 1800-1899 category, even though the authors wrote a century apart.
• Thematic: Thematic reviews of literature are organized around a topic or issue, rather than the progression of time. However, progression of time may still be an important factor in a thematic review. For instance, the sperm whale review could focus on the development of the harpoon for whale hunting. While the study focuses on one topic, harpoon technology, it will still be organized chronologically. The only difference here between a “chronological” and a “thematic” approach is what is emphasized the most: the development of the harpoon or the harpoon technology.But more authentic thematic reviews tend to break away from chronological order. For instance, a thematic review of material on sperm whales might examine how they are portrayed as “evil” in cultural documents. The subsections might include how they are personified, how their proportions are exaggerated, and their behaviors misunderstood. A review organized in this manner would shift between time periods within each section according to the point made.
• Methodological: A methodological approach differs from the two above in that the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the “methods” of the researcher or writer. For the sperm whale project, one methodological approach would be to look at cultural differences between the portrayal of whales in American, British, and French art work. Or the review might focus on the economic impact of whaling on a community. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed. Once you’ve decided on the organizational method for the body of the review, the sections you need to include in the paper should be easy to figure out. They should arise out of your organizational strategy. In other words, a chronological review would have subsections for each vital time period. A thematic review would have subtopics based upon factors that relate to the theme or issue.

Sometimes, though, you might need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. Put in only what is necessary. Here are a few other sections you might want to consider:

• Current Situation: Information necessary to understand the topic or focus of the literature review.
• History: The chronological progression of the field, the literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Methods and/or Standards: The criteria you used to select the sources in your literature review or the way in which you present your information. For instance, you might explain that your review includes only peer-reviewed articles and journals.

Questions for Further Research: What questions about the field has the review sparked? How will you further your research as a result of the review?

Begin composing

Once you’ve settled on a general pattern of organization, you’re ready to write each section. There are a few guidelines you should follow during the writing stage as well. Here is a sample paragraph from a literature review about sexism and language to illuminate the following discussion:

However, other studies have shown that even gender-neutral antecedents are more likely to produce masculine images than feminine ones (Gastil, 1990). Hamilton (1988) asked students to complete sentences that required them to fill in pronouns that agreed with gender-neutral antecedents such as “writer,” “pedestrian,” and “persons.” The students were asked to describe any image they had when writing the sentence. Hamilton found that people imagined 3.3 men to each woman in the masculine “generic” condition and 1.5 men per woman in the unbiased condition. Thus, while ambient sexism accounted for some of the masculine bias, sexist language amplified the effect. (Source: Erika Falk and Jordan Mills, “Why Sexist Language Affects Persuasion: The Role of Homophily, Intended Audience, and Offense,” Women and Language19:2).

Use evidence

In the example above, the writers refer to several other sources when making their point. A literature review in this sense is just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence to show that what you are saying is valid.

Be selective

Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the review’s focus, whether it is thematic, methodological, or chronological.

Use quotes sparingly

Falk and Mills do not use any direct quotes. That is because the survey nature of the literature review does not allow for in-depth discussion or detailed quotes from the text. Some short quotes here and there are okay, though, if you want to emphasize a point, or if what the author said just cannot be rewritten in your own words. Notice that Falk and Mills do quote certain terms that were coined by the author, not common knowledge, or taken directly from the study. But if you find yourself wanting to put in more quotes, check with your instructor.

Summarize and synthesize

Remember to summarize and synthesize your sources within each paragraph as well as throughout the review. The authors here recapitulate important features of Hamilton’s study, but then synthesize it by rephrasing the study’s significance and relating it to their own work.

Keep your own voice

While the literature review presents others’ ideas, your voice (the writer’s) should remain front and center. Notice that Falk and Mills weave references to other sources into their own text, but they still maintain their own voice by starting and ending the paragraph with their own ideas and their own words. The sources support what Falk and Mills are saying.

Use caution when paraphrasing

When paraphrasing a source that is not your own, be sure to represent the author’s information or opinions accurately and in your own words. In the preceding example, Falk and Mills either directly refer in the text to the author of their source, such as Hamilton, or they provide ample notation in the text when the ideas they are mentioning are not their own, for example, Gastil’s. For more information, please see our handout on plagiarism .

Revise, revise, revise

Draft in hand? Now you’re ready to revise. Spending a lot of time revising is a wise idea, because your main objective is to present the material, not the argument. So check over your review again to make sure it follows the assignment and/or your outline. Then, just as you would for most other academic forms of writing, rewrite or rework the language of your review so that you’ve presented your information in the most concise manner possible. Be sure to use terminology familiar to your audience; get rid of unnecessary jargon or slang. Finally, double check that you’ve documented your sources and formatted the review appropriately for your discipline. For tips on the revising and editing process, see our handout on revising drafts .

Works consulted

We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.

Anson, Chris M., and Robert A. Schwegler. 2010. The Longman Handbook for Writers and Readers , 6th ed. New York: Longman.

Jones, Robert, Patrick Bizzaro, and Cynthia Selfe. 1997. The Harcourt Brace Guide to Writing in the Disciplines . New York: Harcourt Brace.

Lamb, Sandra E. 1998. How to Write It: A Complete Guide to Everything You’ll Ever Write . Berkeley: Ten Speed Press.

Rosen, Leonard J., and Laurence Behrens. 2003. The Allyn & Bacon Handbook , 5th ed. New York: Longman.

Troyka, Lynn Quittman, and Doug Hesse. 2016. Simon and Schuster Handbook for Writers , 11th ed. London: Pearson.

You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill

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Writing: Literature Review Basics

• What is Synthesis?
• Organizing Your Research
• Paraphrasing, Summary, or Direct Quotation?
• Introductions
• Conclusions
• All Writing Guides: Home
• CORE Library Home

The Job of the Conclusion

The job of the conclusion is, quite literally, to conclude ... or to wrap things up so the reader feels a sense of closure.  It accomplishes this by stepping back from the specifics in order to view the bigger picture of the document. In other words, it is reminding the reader of the main argument.

Whereas an introduction started out generally and moved towards discussion of a specific focus, the conclusion takes the opposite approach.  It starts by reminding the reader of the contents and importance of your findings and then moves out gradually to more general topics.

For most written assignments, the conclusion is a single paragraph.  It does not introduce any new information; rather, it succinctly restates your chief conclusions and places the importance of your findings within your field.  Depending upon the purpose of the literature review, you may also include a brief statement of future directions or self-reflection.

Here is an easy checklist for writing a conclusion:

 Is the main argument of the paper accurately restated as the first sentence (but is not copied verbatim?

In a literature review, you basicaly want to answer the question, "What did I find out? What conclusions did I come to?"   Giving the reader a one-sentence answer to this question that provides a summary of your findings is a solid way to begin a conclusion.

  What recommendations do you have?

Here you may offer the reader your suggestions on what you think should happen next.  You can make recommendations that are specific to the evidence you have uncovered, or you can make recommendations for future research.  When this area is well done, it links to previous conclusions you have already made and gives the conclusion a finished feeling.

 Did you remind the reader of the importance of the topic and how it can contribute to the knowledge in the field?

Make sure that the paper places its findings in the context of some kind of needed change, relevance, or solution.  If you addressed why the topic was interesting, important, or relevant in your introduction, you can loop back to that here.  Other ways that can be done are to remind the reader of other research you have discussed and how your work builds upon theirs, or what gaps there may yet be to explore.

Keep these items in mind as "what not to do":

 Is there a sense of closure without using words such as "In conclusion?"

If you have to use the words "In conclusion" or similar ones to launch your conclusion so the reader knows the end is near, you've got a problem.  Make sure the reader has a distinct sense that the paper has come to an end without telling them it is ending. It is important to not leave the reader hanging. 

 Did you avoid presenting any new information?

No new ideas should be introduced in the conclusion. It is simply a review of the material that is already present in the paper. The only new idea would be the suggesting of a direction for future research.

Stigmatization of the mentally ill is caused by the public’s belief in myths about the dangerousness of the mentally ill and exposing those myths can reduce stigmatization. At least one-third of the people sampled in one study said that they would both reject socially and fear violence from someone displaying behaviors associated with different mentally illnesses. Other research discovered that this rejection is associated to lack of contact with the mentally ill and that as contact increased, fear of the mentally ill decreased. The direction of the relationship between fear and rejection seems to be that fear (possibly based upon myths about mental illness) causes rejection. Taken as a whole, it appears that exposing these myths as myths increases the acceptance of the mentally ill and that staged contact with a mentally person to expose myths has an even more powerful effect. Caution must be advised, though; Martin et al.’s (2002) and Alexander and Link’s (2003) studies and the first study of Corrigan et al. (2002) were based upon paper and pencil methodologies. And while Corrigan et al.’s (2002) second study involved staged Myths of violence 6 presentations, it was conducted in a college setting with a college sample. Future research should replicate these findings in more natural settings with different populations.

Now let's break that down.

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ON YOUR 1ST ORDER

How to Conclude a Literature Review

By Laura Brown on 6th March 2019

The conclusion of the dissertation literature review focuses on a few critical points,

• Highlight the essential parts of the existing body of literature in a concise way.
• Next, you should analyse the current state of the reviewed literature .
• Explain the research gap for your chosen topic/existing knowledge.
• Now, outline the areas for future study by mentioning main agreements and disagreements in the literature.
• Finally, link the research to existing knowledge .

Now, any of you who have been into research would agree that literature review is a very exhausting process and may stress you during your academic career. It is tougher because it requires you to be organised. We have seen many students asking does a literature review need a conclusion.

Well, the answer is simple, a good literature review will always have a proper ending. But there is nothing to worry about how to write a conclusion for a literature review. Here is a complete guide for you in “four” simple yet convenient steps. These steps can really be valuable in providing an excellent presentation to your literature review help . Furthermore, you can ask us for literature review conclusion examples anytime using our live chat or email option.

Now, without further ado, let’s move towards the steps.

How To Write A Literature Review Conclusion

Get Expert Assistance For Literature Review

Here are four major steps which can help you with how to conclude a literature review with ease.

1. Enlist Key Points

The conclusion can also be said as judgement because it gives a clear view of your work, whether you achieved your targeted objectives or not. Typically, it is not too difficult to conclude a review, but it can be challenging as well if not carried out properly.

It is crucial to find key features which should be engaging and useful as well for a reader. So at first, draft or enlist key factors before moving forward towards initialising your summary.

2. Summarise The Key Features Briefly

This is a most sensitive and important step of a dissertation literature review conclusion, where you should stick to the following things to get the job done efficiently.

• Once you are done drafting the important points , here you should mention them briefly.
• You can also take the liberty to agree or disagree with whatever literature you have gone through.
• Make sure you don’t drag your arguments while counter-arguing. Keeping your points specific is key.
• Describe, in one to two lines, how you addressed the previously identified gap .
• It is also important to point out the lapses you have noticed in previous authors’ work. Those lapses could be a misquotation of figures, a wrong pattern of research and so on.
• Alongside this, discuss existing theories and methods to build a framework for your research.

3. Educational Implications Of The Reviewed Literature

After mentioning the key factors, it is suggested to put implications to the already reviewed research. Like, as identifying problems in the already done research and giving recommendations on how these problems can be resolved.

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4. Indicating Room For Future Research

After completing the whole analysis of the particular research, you will be capable of identifying the work which can be done in future. You can also leave some gaps for future researchers so others can extend your work. This will be the final step, and this is how to end a literature review.

Tips That Can Enlighten Your Conclusion

We hope that things are very clear to you on how to write a conclusion for a literature review. If you want it to be even better and more meaningful, then you should keep the below points in mind.

• It should not be burdened with an unnecessary chain of details.
• It should be as precise and easy to understand as possible.
• You should mention important key points and findings .
• Make sure to put all points in a flow so the reader can understand your research in one go.
• Do not add anything from your own.

“Simply put, touch the prominent factors and leave them unexplained here”.

Get Help to Conclude Your Literature Review

If you are able to keep your focus around these steps and mentioned points, believe us, you will never ask anyone how to conclude literature review.

Looking At Literature Review Conclusion Example

Below are three examples which will help you understand how to conclude a literature review.

1. Firstly, you should summarise the important aspects and evaluate the current state of the existing literature.

Overall, the findings from this literature review highlight the need for further research to address the gaps in knowledge on the effectiveness of mindfulness-based interventions for reducing symptoms of anxiety and depression in college students.

2. Now, along with mentioning the gaps, come up with your approach to future study.

Therefore, to address this gap in the literature, we incorporated larger and more diverse samples, used standardised measures of mindfulness and mental health outcomes, and included longer follow-up periods to assess the long-term effects of mindfulness-based interventions on anxiety and depression.

3. Now summarise on how your findings will contribute to the particular field by linking it to the existing knowledge.

The findings from the study will provide important insights for researchers, clinicians, and educators interested in developing and implementing effective interventions to promote mental health and well-being among college students, and highlight the need for further research to establish the effectiveness of mindfulness-based interventions in this population.

We hope that these examples will bring in more clarification and you can have a better idea about the literature review conclusion.

What basically is a literature review?

What are the 3 primary parts of a literature review, what are the goals of writing a literature review.

There are four primary objectives of writing a literature review:

1. Determining the background from the previous scholarly literature related to the topic.

2. Identifying the gaps between literature to boost further research.

3. Analysing if the theory is applicable and associating a suitable methodology.

Why is a literature review conclusion necessary?

• https://azhin.org/cummings/basiclitreview/conclusions
• https://www.citewrite.qut.edu.au/write/writing-well/litreview.html
• https://psychology.ucsd.edu/undergraduate-program/undergraduate-resources/academic-writing-resources/writing-research-papers/writing-lit-review.html
• https://students.unimelb.edu.au/academic-skills/resources/report-writing/reviewing-the-literature

Laura Brown, a senior content writer who writes actionable blogs at Crowd Writer.

Conducting a Literature Review

• Getting Started
• Define your Research Question
• Finding Sources
• Evaluating Sources
• Organizing the Review
• Cite and Manage your Sources

Introduction

Once you have your literature review planned out, you are ready to begin writing! Good organization and a clear focus are key to writing a successful academic paper of any kind, which is why the previous steps in this guide are so important; the more thorough you are with each of the preceding elements of writing the literature review, the easier this final step will be.

A literature review is organized into an introduction, multiple body paragraphs, and a conclusion. This format should be familiar to you, as it is the general outline of most academic essays; what is new and exciting about this literature review is the information you've gathered in your research and synthesized in your organization and outlining process.

Remember, if you ever need help with writing an essay of any kind, the ACPHS Writing Center is here to help! You can book an appointment with one of the peer tutors or reach out by email. The Library is also here to provide assistance with your assignments, particularly finding or citing resources.

Additional Resources

• Write a Literature Review by the University of Guelph McLaughlin Library

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Make an appointment

Intro Paragraph & Thesis

Introductory paragraphs can be the most challenging part of writing a paper. Instead of laying out the evidence (or in the case of a literature review, analyzing your resources), you must first provide background information and context for the topic, discuss the body of literature in general as well as the scope of your review, and give a brief outline of how you will organize the review.

It is generally a good idea to open an introduction with a hook, or an interesting first sentence. This could be a statistic or fact about the topic that you find relevant, a rhetorical question that will be answered in the rest of the introduction, or even an appropriate anecdote. The point of a strong hook is to catch the reader's attention; for a literature review, it can help get the reader invested in the research around your topic, as well as your analysis of it.

Some authors prefer to write their introductory paragraph after completing the body of the essay, finding it easier to summarize what will be shared with the reader after it has already been written. There is no right or wrong order for crafting your paper, so if this method appeals to you then you should make use of it. However, with appropriately detailed planning it can be simple to write out an introduction prior to the body. Using an outline  (using the methods provided by Walden University, for example) can make writing the introduction and the entire essay much simpler.

Your literature review's introduction should contain four major elements:

• Establishing the topic, including providing background information and any necessary definitions to make sure your reader has all the context necessary to understand the rest of the literature review
• The trends or themes of the research that you noticed while compiling your sources, including any that you will use to organize your literature
• The purpose, criteria, and scope of the literature review: how will the literature be organized? What is your reason for examining this topic? What will you be analyzing about the sources (comparing/contrasting research methodology, conclusions, etc.)? Is there any literature you decided not to include -- if so, what disqualified it from the review?
• Introduce your thesis statement by drawing on the previous 3 components of the introduction to state what you discovered about the literature on this topic. Specifically, the thesis should answer where the current literature's strengths and weaknesses lie, and where additional research may be needed

The purpose of the introduction is to make sure that your reader has all the information they need to understand and appreciate your literature review, and to provide them a general blueprint of the analysis and arguments you will be making.

• 5 Questions to Strengthen Your Thesis Statement by the University of Guelph Digital Learning Commons

Body Paragraphs

With the introduction out of the way -- or perhaps even before you've written the introduction -- it's time to examine the literature you've gathered. We established how to organize the literature in the previous section of this guide, and that organization will serve as the framework for the body paragraphs. For example, if you organized your literature into themes, then each theme would serve as its own paragraph, in which you'd compare and contrast the sources within each theme; if you organized it by methodology or historical era, each of those would be a body paragraph.

As you write your literature analyses, keep the following recommendations in mind, provided by Shona McCombes at Scribbr :

Summarize  and synthesize:  give an overview of the main points of each source and combine them into a coherent whole Analyze and interpret:  don’t just  paraphrase  other researchers—add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole Critically evaluate:  mention the strengths and weaknesses of your sources Write in well-structured paragraphs:  use  transition words  and  topic sentences  to draw connections, comparisons and contrasts

Your summary of each source can be as detailed as is appropriate, based on how important the source is to the overall literature or how much analysis you have to perform on it. In general, the more significant a source is to your review, the more time should be devoted to summarizing and analyzing it.

While looking at individual sources, remember to keep connecting them back to the theme of the body paragraph and the overall thesis; explaining their relevance in a particular section of literature helps the reader follow along and better understand your overall arguments.

Other useful tips to keep in mind when writing your body paragraphs, provided by the Writing Center of the University of North Carolina at Chapel Hill :

• Use evidence to support your claims
• Be selective, and focus on the most important points for each piece of literature rather than trying to describe everything
• Use quotes when appropriate, but know that literature reviews do not frequently require direct quotations
• Paraphrase accurately
• Literature Reviews by the University of North Carolina at Chapel Hill's Writing Center

Conclusion & Reviewing Your Paper

Concluding Paragraph

A conclusion is used to provide further reinforcement of the arguments presented throughout the paper. In general, this consists of briefly summarizing the body paragraphs and reasserting their connection to your thesis. This is also good practice for a literature review; in addition, your conclusion should again summarize the broad trends of the research on your topic, as well as any opportunities for additional or more thorough research that you've found. 

Below are some helpful recommendations for writing conclusions, compiled from advice explained in more detail in the links below:

• Address the broader implications of the existing research, and why it is important to close the gaps you evaluated during your literature review
• Include a quotation or fact that effectively illustrates your thesis in a provocative or interesting way
• Use simple, clear language without jargon
• Reestablish your thesis and its connection with the literature reviewed

Your goal with the concluding paragraph of your literature review should be to leave the reader with a firm understanding of the existing literature on your topic, where additional research may be necessary, and why it matters.

Revising Your Literature Review

Revision is a process that goes beyond simply correcting spelling and grammar mistakes -- though proofreading is an important part of the writing process as well. The purpose of revising your literature review before submission is to look at it the way your reader will and pick up on any potential leaps of logic, unclear explanations, or shoddy evidence. The revision process should not begin immediately after finishing the paper; whenever possible, wait a few hours or days before looking at your draft, so that you can approach it with fresh eyes. 

When revising, focus on major issues with the paper such as organization, clarity, and thoroughness. Trying to both revise your writing and proofread it for small spelling or grammar issues may distract you from more important areas that could be improved. Ask yourself if your thesis is well-defended by the body paragraphs, and if you still agree with the conclusions you stated in the introduction. If more or better arguments are needed, find places in the body paragraphs to add evidence or make clearer connections to your thesis. Focus on the flow of the review; does each body paragraph move naturally into the next one? Do your paragraphs need to be reordered or restructured?

After major revisions are done, it is time to proofread for spelling, grammar, and general writing errors. Try reading the paper out loud and seeing where your word choice could be strengthened or a run-on sentence could be amended.

It can sometimes be difficult to revise an essay on your own, so consider booking an appointment with the ACPHS Writing Center to go over your writing with a tutor. Friends, classmates, or your professor can also be useful sources of feedback, and if possible try to get as many different readers to look over your writing and provide insight.

• Revising Drafts by the University of North Carolina at Chapel Hill Writing Center
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In a short paper—even a research paper—you don’t need to provide an exhaustive summary as part of your conclusion. But you do need to make some kind of transition between your final body paragraph and your concluding paragraph. This may come in the form of a few sentences of summary. Or it may come in the form of a sentence that brings your readers back to your thesis or main idea and reminds your readers where you began and how far you have traveled.

So, for example, in a paper about the relationship between ADHD and rejection sensitivity, Vanessa Roser begins by introducing readers to the fact that researchers have studied the relationship between the two conditions and then provides her explanation of that relationship. Here’s her thesis: “While socialization may indeed be an important factor in RS, I argue that individuals with ADHD may also possess a neurological predisposition to RS that is exacerbated by the differing executive and emotional regulation characteristic of ADHD.”

In her final paragraph, Roser reminds us of where she started by echoing her thesis: “This literature demonstrates that, as with many other conditions, ADHD and RS share a delicately intertwined pattern of neurological similarities that is rooted in the innate biology of an individual’s mind, a connection that cannot be explained in full by the behavioral mediation hypothesis.”  

Highlight the “so what”  

At the beginning of your paper, you explain to your readers what’s at stake—why they should care about the argument you’re making. In your conclusion, you can bring readers back to those stakes by reminding them why your argument is important in the first place. You can also draft a few sentences that put those stakes into a new or broader context.

In the conclusion to her paper about ADHD and RS, Roser echoes the stakes she established in her introduction—that research into connections between ADHD and RS has led to contradictory results, raising questions about the “behavioral mediation hypothesis.”

She writes, “as with many other conditions, ADHD and RS share a delicately intertwined pattern of neurological similarities that is rooted in the innate biology of an individual’s mind, a connection that cannot be explained in full by the behavioral mediation hypothesis.”  

Leave your readers with the “now what”  

After the “what” and the “so what,” you should leave your reader with some final thoughts. If you have written a strong introduction, your readers will know why you have been arguing what you have been arguing—and why they should care. And if you’ve made a good case for your thesis, then your readers should be in a position to see things in a new way, understand new questions, or be ready for something that they weren’t ready for before they read your paper.

In her conclusion, Roser offers two “now what” statements. First, she explains that it is important to recognize that the flawed behavioral mediation hypothesis “seems to place a degree of fault on the individual. It implies that individuals with ADHD must have elicited such frequent or intense rejection by virtue of their inadequate social skills, erasing the possibility that they may simply possess a natural sensitivity to emotion.” She then highlights the broader implications for treatment of people with ADHD, noting that recognizing the actual connection between rejection sensitivity and ADHD “has profound implications for understanding how individuals with ADHD might best be treated in educational settings, by counselors, family, peers, or even society as a whole.”

To find your own “now what” for your essay’s conclusion, try asking yourself these questions:

• What can my readers now understand, see in a new light, or grapple with that they would not have understood in the same way before reading my paper? Are we a step closer to understanding a larger phenomenon or to understanding why what was at stake is so important?  
• What questions can I now raise that would not have made sense at the beginning of my paper? Questions for further research? Other ways that this topic could be approached?  
• Are there other applications for my research? Could my questions be asked about different data in a different context? Could I use my methods to answer a different question?  
• What action should be taken in light of this argument? What action do I predict will be taken or could lead to a solution?  
• What larger context might my argument be a part of?  

What to avoid in your conclusion  

• a complete restatement of all that you have said in your paper.  
• a substantial counterargument that you do not have space to refute; you should introduce counterarguments before your conclusion.  
• an apology for what you have not said. If you need to explain the scope of your paper, you should do this sooner—but don’t apologize for what you have not discussed in your paper.  
• fake transitions like “in conclusion” that are followed by sentences that aren’t actually conclusions. (“In conclusion, I have now demonstrated that my thesis is correct.”)
• picture_as_pdf Conclusions

Essays, Literature Reviews and Reports - Skills Guide

Literature review.

• Downloadable Resources
• Further Reading

What is a literature review?

A literature review is a collection of literature that is analysed (reviewed) and compared against each other to demonstrate an understanding of a topic. In a literature review you identify relevant theories and previous research in the area. Bell states that  "literature reviews should be succinct and.. give a picture of the state of knowledge and major questions in your topic area."

Literature reviews are usually a part of a dissertation, although some modules may require a standalone literature review.

Why are literature reviews important?

Literature reviews are important as they allow you to gain a thorough awareness and understanding of current work and perspectives in a research area to support and justify your research, as well as illustrating that there is a research gap and assisting in the analysis and interpretation of data.

What should I put into a literature review?

• The historical context.
• The contemporary context of your research.
• A discussion of the relevant underpinning concepts and theories.
• Definitions of the key terminology used in your own work.
• Current research in the field that can be challenged or extended by your own research.
• Justification of the significance of your research.

How do I structure a literature review?

Look carefully at what is expected from you for your literature review. Sometimes they might focus heavily on one piece of literature, while others may focus on two or three, and some would like a vast body of literature to be included. Whatever the expectation, they usually follow the same structure as an essay:

10% Introduction

80% Main Body

10% Conclusion

The introduction should explain how your literature review is organised.

The main body should be made up of headings and sub headings that map out your argument.

The conclusion should summarise the key arguments in a concise way.

When should I start writing my literature review?

Starting writing your literature review as early as possible can help you in understanding the research and understanding how it will be used. This will help in creating an overall structure when writing later versions of the literature review and in comparing and linking different pieces of research. 

There are example essay extracts available on Do It Write ( click here ) to help you understand what they're asking from you. 

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Literature Review: Conducting & Writing

• Sample Literature Reviews
• Steps for Conducting a Lit Review
• Finding "The Literature"
• Organizing/Writing
• APA Style This link opens in a new window
• Chicago: Notes Bibliography This link opens in a new window
• MLA Style This link opens in a new window

Sample Lit Reviews from Communication Arts

Have an exemplary literature review.

• Literature Review Sample 1
• Literature Review Sample 2
• Literature Review Sample 3

Have you written a stellar literature review you care to share for teaching purposes?

Are you an instructor who has received an exemplary literature review and have permission from the student to post?

Please contact Britt McGowan at [email protected] for inclusion in this guide. All disciplines welcome and encouraged.

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How to Write a Literature Review

As every student knows, writing informative essay and research papers is an integral part of the educational program. You create a thesis, support it using valid sources, and formulate systematic ideas surrounding it. However, not all students know that they will also have to face another type of paper known as a Literature Review in college. Let's take a closer look at this with our custom essay writer .

Literature Review Definition

As this is a less common academic writing type, students often ask: "What is a literature review?" According to the definition, a literature review is a body of work that explores various publications within a specific subject area and sometimes within a set timeframe.

This type of writing requires you to read and analyze various sources that relate to the main subject and present each unique comprehension of the publications. Lastly, a literature review should combine a summary with a synthesis of the documents used. A summary is a brief overview of the important information in the publication; a synthesis is a re-organization of the information that gives the writing a new and unique meaning.

Typically, a literature review is a part of a larger paper, such as a thesis or dissertation. However, you may also be given it as a stand-alone assignment.

The Purpose

The main purpose of a literature review is to summarize and synthesize the ideas created by previous authors without implementing personal opinions or other additional information.

However, a literature review objective is not just to list summaries of sources; rather, it is to notice a central trend or principle in all of the publications. Just like a research paper has a thesis that guides it on rails, a literature review has the main organizing principle (MOP). The goal of this type of academic writing is to identify the MOP and show how it exists in all of your supporting documents.

Why is a literature review important? The value of such work is explained by the following goals it pursues:

• Highlights the significance of the main topic within a specific subject area.
• Demonstrates and explains the background of research for a particular subject matter.
• Helps to find out the key themes, principles, concepts, and researchers that exist within a topic.
• Helps to reveal relationships between existing ideas/studies on a topic.
• Reveals the main points of controversy and gaps within a topic.
• Suggests questions to drive primary research based on previous studies.

Here are some example topics for writing literature reviews:

• Exploring racism in "To Kill a Mockingbird," "The Adventures of Huckleberry Finn," and "Uncle Tom's Cabin."
• Isolationism in "The Catcher in the Rye," "Frankenstein," and "1984"
• Understanding Moral Dilemmas in "Crime and Punishment," "The Scarlet Letter," and "The Lifeboat"
• Corruption of Power in "Macbeth," "All the King's Men," and "Animal Farm"
• Emotional and Physical survival in "Lord of the Flies," "Hatchet," and "Congo."

How Long Is a Literature Review?

When facing the need to write a literature review, students tend to wonder, "how long should a literature review be?" In some cases, the length of your paper's body may be determined by your instructor. Be sure to read the guidelines carefully to learn what is expected from you.

Keeping your literature review around 15-30% of your entire paper is recommended if you haven't been provided with specific guidelines. To give you a rough idea, that is about 2-3 pages for a 15-page paper. In case you are writing a literature review as a stand-alone assignment, its length should be specified in the instructions provided.

Literature Review Format: APA, MLA, and Chicago

The essay format you use should adhere to the citation style preferred by your instructor. Seek clarification from your instructor for several other components as well to establish a desired literature review format:

• How many sources should you review, and what kind of sources should they be (published materials, journal articles, or websites)?
• What format should you use to cite the sources?
• How long should the review be?
• Should your review consist of a summary, synthesis, or a personal critique?
• Should your review include subheadings or background information for your sources?

If you want to format your paper in APA style, then follow these rules:

• Use 1-inch page margins.
• Unless provided with other instructions, use double-spacing throughout the whole text.
• Make sure you choose a readable font. The preferred font for APA papers is Times New Roman set to 12-point size.
• Include a header at the top of every page (in capital letters). The page header must be a shortened version of your essay title and limited to 50 characters, including spacing and punctuation.
• Put page numbers in the upper right corner of every page.
• When shaping your literature review outline in APA, don't forget to include a title page. This page should include the paper's name, the author's name, and the institutional affiliation. Your title must be typed with upper and lowercase letters and centered in the upper part of the page; use no more than 12 words, and avoid using abbreviations and useless words.

For MLA style text, apply the following guidelines:

• Double your spacing across the entire paper.
• Set ½-inch indents for each new paragraph.
• The preferred font for MLA papers is Times New Roman set to 12-point size.
• Include a header at the top of your paper's first page or on the title page (note that MLA style does not require you to have a title page, but you are allowed to decide to include one). A header in this format should include your full name; the name of your instructor; the name of the class, course, or section number; and the due date of the assignment.
• Include a running head in the top right corner of each page in your paper. Place it one inch from the page's right margin and half an inch from the top margin. Only include your last name and the page number separated by a space in the running head. Do not put the abbreviation p. before page numbers.

Finally, if you are required to write a literature review in Chicago style, here are the key rules to follow:

• Set page margins to no less than 1 inch.
• Use double spacing across the entire text, except when it comes to table titles, figure captions, notes, blockquotes, and entries within the bibliography or References.
• Do not put spaces between paragraphs.
• Make sure you choose a clear and easily-readable font. The preferred fonts for Chicago papers are Times New Roman and Courier, set to no less than 10-point size, but preferably to 12-point size.
• A cover (title) page should include your full name, class information, and the date. Center the cover page and place it one-third below the top of the page.
• Place page numbers in the upper right corner of each page, including the cover page.

Read also about harvard format - popular style used in papers.

Structure of a Literature Review

How to structure a literature review: Like many other types of academic writing, a literature review follows a typical intro-body-conclusion style with 5 paragraphs overall. Now, let’s look at each component of the basic literature review structure in detail:

• Introduction

You should direct your reader(s) towards the MOP (main organizing principle). This means that your information must start from a broad perspective and gradually narrow down until it reaches your focal point.

Start by presenting your general concept (Corruption, for example). After the initial presentation, narrow your introduction's focus towards the MOP by mentioning the criteria you used to select the literature sources you have chosen (Macbeth, All the King's Men, and Animal Farm). Finally, the introduction will end with the presentation of your MOP that should directly link it to all three literature sources.

Body Paragraphs

Generally, each body paragraph will focus on a specific source of literature laid out in the essay's introduction. As each source has its own frame of reference for the MOP, it is crucial to structure the review in the most logically consistent way possible. This means the writing should be structured chronologically, thematically or methodologically.

Chronologically

Breaking down your sources based on their publication date is a solid way to keep a correct historical timeline. If applied properly, it can present the development of a certain concept over time and provide examples in the form of literature. However, sometimes there are better alternatives we can use to structure the body.

Thematically

Instead of taking the "timeline approach," another option can be looking at the link between your MOP and your sources. Sometimes, the main idea will just glare from a piece of literature. Other times, the author may have to seek examples to prove their point. An experienced writer will usually present their sources by order of strength. For example, in "To Kill A Mockingbird," the entire novel was centralized around racism; in "The Adventures of Huckleberry Finn," racism was one of many themes.

Methodologically

As made obvious by the terminology, this type of structuring focuses on the methods used to present the central concept. For example, in "1984", George Orwell uses the law-and-order approach and shows the dangers of a dystopia for a social species.

In "Frankenstein," Mary Shelley exposes the character's physical traits as repulsive and horrifying, forcing him to suffer in an isolated environment. By showcasing the various methods used to portray the MOP, the writer can compare them based on things like severity, ethicality, and overall impact.

After presenting your key findings in the body paragraphs, there are 3 final objectives to complete in the essay's conclusion. First, the author should summarize the findings they have made or found, in other words, and briefly answer the question: "What have you learned?"

After discussing that information, the next step is to present the significance of the information about our current world today. In other words, how can the reader take the information and apply it to today's society? From that point, we finish off with a breadcrumb trail.

As the author, you want to leave the readers' trail of thought within the actual essay topic. This provides them with a means of further investigation—meaning that the reader may consider where the discussion will go next.

Writing an Outline for a Literature Review

Students often underestimate the importance of planning the structure of their papers in advance. However, this is not a wise approach. Having a rough APA literature review outline (or other style outlines) will not only help you follow the right format and structure but will also make the writing process simpler and help ensure that you include all of the important information without missing anything.

How to write a literature review outline: As you already know from the Structure section of this guide, every part of your literature review performs its own important role. Therefore, you should create your outline while keeping the general introduction-body-conclusion structure in mind and ensuring that each section meets its own objectives. However, it is important to remember that a literature review outline is slightly different from outlines of other types of essays because it does not provide new information. Instead, it focuses on existing studies relevant to the main topic. ‍

Here is a literature review outline example on the subject of the Ebola virus to help you get it right:

• Introduce the general topic. Provide background information on the Ebola virus: genome, pathogenesis, transmission, epidemiology, treatment, etc.
• Shape the main research question: What is the potential role of arthropods (mechanical or biological vectors) in the distribution of the Ebola virus?
• Methodology: For example, the information was searched through X databases to find relevant research articles about the Ebola virus and arthropods' role in its spreading. The data was extracted using a standardized form.
• Expected outcomes
• Overall trends in the literature on this topic: While the natural reservoir of the virus is still not known with certainty, many researchers believe that arthropods (and fruit bats, in particular) pay a significant role in the distribution of the virus.
• Subject 1: A brief overview of the particular piece of literature in general terms; an analysis of the key aspects of the study; a review of the research questions, methods, procedures, and outcomes; and an overview of the strong and weak points, gaps, and contradictions.
• Subject 2: A brief overview of the particular piece of literature in general terms; an analysis of the key aspects of the study; a review of the research questions, methods, procedures, and outcomes; and an overview of the strong and weak points, gaps, and contradictions.
• Subject 3:  A brief overview of the particular piece of literature in general terms; an analysis of the key aspects of the study; a review of the research questions, methods, procedures, and outcomes; and an overview of the strong and weak points, gaps, and contradictions.
• Indicate the relationships between the pieces of literature discussed. Emphasize key themes, common patterns, and trends. Talk about the pros and cons of the different approaches taken by the authors/researchers.
• State which studies seem to be the most influential.
• Emphasize the major contradictions and points of disagreement. Define the gaps still to be covered (if any).
• If applicable: define how your own study will contribute to further disclosure of the topic.

Hopefully, this sample outline will help you to structure your own paper. However, if you feel like you need some more advice on how to organize your review, don’t hesitate to search for more literature review outline examples in APA or other styles on the Web, or simply ask our writers to get a dissertation help .

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How to Write a Good Literature Review

Whether you are writing a literature review within the framework of a large research project (e.g. thesis, dissertation, or other) or as a stand-alone assignment, the approach you should take to writing generally remains the same.

Whether you are writing a literature review within the framework of a large research project (e.g., thesis, dissertation, or other) or as a stand-alone assignment, the approach you should take to writing generally remains the same.

Now, as you know about the general rules and have a basic literature review outline template, let's define the steps to take to handle this task right with our service:

Step 1: Identifying the Topic

This is probably the only matter you may approach differently depending on whether your literature review comes within a research paper or a separate assignment altogether. If you are creating a literature review as a part of another work, you need to search for literature related to your main research questions and problems. Respectively, if you are writing it as a stand-alone task, you will have to pick a relevant topic and central question upon which you will collect the literature. Earlier in this guide, we suggested some engaging topics to guide your search.

Step 2: Conducting Research

When you have a clearly defined topic, it is time to start collecting literature for your review. We recommend starting by compiling a list of relevant keywords related to your central question—to make the entire research process much simpler and help you find relevant publications faster.

When you have a list of keywords, use them to search for valid and relevant sources. At this point, be sure to use only trusted sources, such as ones from university libraries, online scientific databases, etc.

Once you have found some sources, be sure to define whether or not they are actually relevant to your topic and research question. To save time, you can read abstracts to get general ideas of what the papers are about instead of the whole thing.

Pro Tip: When you finally find a few valid publications, take a look at their bibliographies to discover other relevant sources as well.

Step 3: Assess and Prioritize Sources

Throughout your research, you will likely find plenty of relevant literature to include in your literature review. At this point, students often make the mistake of trying to fit all the collected sources into their reviews. Instead, we suggest looking at what you've collected once more, evaluating the available sources, and selecting the most relevant ones. You most likely won't be able to read everything you find on a given topic and then be able to synthesize all of the sources into a single literature review. That's why prioritizing them is important.

To evaluate which sources are worth including in your review, keep in mind the following criteria:

• Credibility;
• Innovation;
• Key insights;

Furthermore, as you read the sources, don’t forget to take notes on everything you can incorporate into the review later. And be sure to get your citations in place early on. If you cite the selected sources at the initial stage, you will find it easier to create your annotated bibliography later on.

Step 4: Identify Relationships, Key Ideas, and Gaps

Before you can move on to outlining and writing your literature review, the final step is determining the relationships between the studies that already exist. Identifying the relationships will help you organize the existing knowledge, build a solid literature outline, and (if necessary) indicate your own research contribution to a specific field.

Some of the key points to keep an eye out for are:

• Main themes;
• Contradictions and debates;
• Influential studies or theories;
• Trends and patterns;

Here are a few examples: Common trends may include a focus on specific groups of people across different studies. Most researchers may have increased interest in certain aspects of the topic regarding key themes. Contradictions may include some disagreement concerning the theories and outcomes of a study. And finally, gaps most often refer to a lack of research on certain aspects of a topic.

Step 5: Make an Outline

Although students tend to neglect this stage, outlining is one of the most important steps in writing every academic paper. This is the easiest way to organize the body of your text and ensure that you haven't missed anything important. Besides, having a rough idea of what you will write about in the paper will help you get it right faster and more easily. Earlier in this guide, we already discussed the basic structure of a literature review and gave you an example of a good outline. At this workflow stage, you can use all of the knowledge you've gained from us to build your own outline.

Step 6: Move on to Writing

Having found and created all of your sources, notes, citations, and a detailed outline, you can finally get to the writing part of the process. At this stage, all you need to do is follow the plan you've created and keep in mind the overall structure and format defined in your professor's instructions.

Step 7: Adding the Final Touches

Most students make a common mistake and skip the final stage of the process, which includes proofreading and editing. We recommend taking enough time for these steps to ensure that your work will be worth the highest score. Do not underestimate the importance of proofreading and editing, and allocate enough time for these steps.

Pro Tip: Before moving on to proofreading and editing, be sure to set your literature review aside for a day or two. This will give you a chance to take your mind off it and then get back to proofreading with a fresh perspective. This tip will ensure that you won't miss out on any gaps or errors that might be present in your text.

These steps will help you create a top-notch literature review with ease! Want to get more advice on how to handle this body of work? Here are the top 3 tips you need to keep in mind when writing a literature review:

1. Good Sources

When working on a literature review, the most important thing any writer should remember is to find the best possible sources for their MOP. This means that you should select and filter through about 5-10 different options while doing initial research.

The stronger a piece of literature showcases the central point, the better the quality of the entire review.

2. Synthesize The Literature

Make sure to structure the review in the most effective way possible, whether it be chronologically, thematically, or methodologically. Understand what exactly you would like to say, and structure the source comparison accordingly.

3. Avoid Generalizations

Remember that each piece of literature will approach the MOP from a different angle. As the author, make sure to present the contrasts in approaches clearly and don't include general statements that offer no value.

Literature Review Examples

You can find two well-written literature reviews by the EssayPro writing team below. They will help you understand what the final product of a literature review should ideally look like.

The first literature review compares monolingual and bilingual language acquisition skills and uses various sources to prove its point:

The second literature review compares the impact of fear and pain on a protagonist’s overall development in various settings:

Both reviews will help you sharpen your skills and provide good guidelines for writing high-quality papers.

Get Help from an Essay Writer

Still aren’t sure whether you can handle literature review writing on your own? No worries because you can pay for essay writing and our service has got you covered! Boost your grades is to place an order in a few quick clicks and we will satisfy your write my paper request.

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How to Write a Conclusion to a Literary Essay

Last Updated: July 3, 2023 Fact Checked

This article was co-authored by Stephanie Wong Ken, MFA . Stephanie Wong Ken is a writer based in Canada. Stephanie's writing has appeared in Joyland, Catapult, Pithead Chapel, Cosmonaut's Avenue, and other publications. She holds an MFA in Fiction and Creative Writing from Portland State University. There are 9 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 79,615 times.

A literary essay should analyze and evaluate a work of literature or an aspect of a work of literature. You may be required to write a literary essay for Language Arts class or as an assignment for an English Literature course. After a lot of hard work, you may have the majority of your literary essay done and be stuck on the conclusion. A strong conclusion will restate the thesis statement and broaden the scope of the essay in four to six sentences. You should also have an effective last sentence in the essay so you can wrap it up on a high note.

Reworking Your Thesis Statement

• For example, maybe your original thesis statement was, “Though there are elements of tragedy in Shakespeare’s A Midsummer Night’s Dream , the structure, themes, and staging of the play fall into the genre of comedy.”
• You may then rephrase your thesis statement by shifting around some of the language in the original and by using a more precise word choice. For example, the rephrased thesis statement may be, “While there are tragic moments in Shakespeare’s A Midsummer Night’s Dream , the structure, themes, and staging of the play fit within the genre of comedy.”

• You may then revise it to better reflect your essay as a whole, “While tragic events do occur in Shakespeare’s A Midsummer Night’s Dream , the three-act structure, the themes of magic and dreams, as well as the farcical staging of the play indicate that it fits in the genre of comedy.”
• Keep in mind if you make major revisions to your thesis statement, it should only be done to reflect the rest of your essay as a whole. Make sure the original thesis statement in your introduction still compliments or reflects the revised thesis statement in your conclusion.

• You do not need to put “In conclusion,” “In summary,” or “To conclude” before your thesis statement to start the conclusion. This can feel too formal and stilted. Instead, start a new paragraph and launch right into your rephrased thesis statement at the beginning of the conclusion.

Writing the Middle Section of the Conclusion

• For example, you may have a sentence about how the staging of the play affects the genre of the play in your introduction. You could then rephrase this sentence and include it in your conclusion.
• If you read over your introduction and realize some of your ideas have shifted in your body paragraphs, you may need to revise your introduction and use the revisions to then write the middle section of the conclusion.

• For example, maybe you focus on the theme of magic in Shakespeare’s A Midsummer Night’s Dream in the body section of your essay. You can then reiterate the theme of magic by using an image from the play that illustrates the magical element of the text.

• For example, if your essay focuses on how the theme of love in Shakespeare’s A Midsummer Night’s Dream , you may include a quote from the text that illustrates this theme.

• For example, if you are writing an essay about Harper Lee's To Kill A Mockingbird , you may answer the question “so what?” by thinking about how and why Harper Lee's novel discusses issues of race and identity in the South. You could then use your response in the conclusion of the essay.

• For example, you may summarize your essay by noting, "An analysis of scenes between white characters and African-American characters in the novel, as done in this essay, make it clear that Lee is addressing questions of race and identity in the South head-on."

Wrapping Up the Conclusion

• For example, if the focus of your essay is the theme of magic in the text, you may end with an image for the text that includes a magical element that is important to the main character.

• Read over your last sentence and remove any words that seem unnecessary or confusing. Simplify the last sentence of your conclusion so it is concise and to the point.

• For example, you may connect an essay about Harper Lee's To Kill A Mockingbird to modern issues around African-American rights in America.
• Avoid making overblown statements in the conclusion in an attempt to sum up your thoughts. Connecting your essay to a larger context is fine. Trying to connect your essay to vague ideas like “world suffering” or “the wage gap” will only confuse your reader and weaken your conclusion.

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• ↑ https://human.libretexts.org/Bookshelves/Literature_and_Literacy/Writing_and_Critical_Thinking_Through_Literature_(Ringo_and_Kashyap)/12%3A_Writing_About_Literature/12.06%3A_Literary_Thesis_Statements
• ↑ https://writingcenter.unc.edu/tips-and-tools/thesis-statements/
• ↑ https://writingcenter.unc.edu/tips-and-tools/conclusions/
• ↑ https://libguides.usc.edu/writingguide/academicwriting
• ↑ https://lsa.umich.edu/sweetland/undergraduates/writing-guides/how-do-i-write-an-intro--conclusion----body-paragraph.html
• ↑ https://academicguides.waldenu.edu/writingcenter/writingprocess/conclusions
• ↑ https://libguides.usc.edu/writingguide/conclusion
• ↑ https://writingcenter.fas.harvard.edu/pages/ending-essay-conclusions
• ↑ https://www.unr.edu/writing-speaking-center/student-resources/writing-speaking-resources/editing-and-proofreading-techniques

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How to write a literature review introduction (+ examples)

The introduction to a literature review serves as your reader’s guide through your academic work and thought process. Explore the significance of literature review introductions in review papers, academic papers, essays, theses, and dissertations. We delve into the purpose and necessity of these introductions, explore the essential components of literature review introductions, and provide step-by-step guidance on how to craft your own, along with examples.

Why you need an introduction for a literature review

When you need an introduction for a literature review, what to include in a literature review introduction, examples of literature review introductions, steps to write your own literature review introduction.

A literature review is a comprehensive examination of the international academic literature concerning a particular topic. It involves summarizing published works, theories, and concepts while also highlighting gaps and offering critical reflections.

In academic writing , the introduction for a literature review is an indispensable component. Effective academic writing requires proper paragraph structuring to guide your reader through your argumentation. This includes providing an introduction to your literature review.

It is imperative to remember that you should never start sharing your findings abruptly. Even if there isn’t a dedicated introduction section .

Instead, you should always offer some form of introduction to orient the reader and clarify what they can expect.

There are three main scenarios in which you need an introduction for a literature review:

• Academic literature review papers: When your literature review constitutes the entirety of an academic review paper, a more substantial introduction is necessary. This introduction should resemble the standard introduction found in regular academic papers.
• Literature review section in an academic paper or essay: While this section tends to be brief, it’s important to precede the detailed literature review with a few introductory sentences. This helps orient the reader before delving into the literature itself.
• Literature review chapter or section in your thesis/dissertation: Every thesis and dissertation includes a literature review component, which also requires a concise introduction to set the stage for the subsequent review.

You may also like: How to write a fantastic thesis introduction (+15 examples)

It is crucial to customize the content and depth of your literature review introduction according to the specific format of your academic work.

In practical terms, this implies, for instance, that the introduction in an academic literature review paper, especially one derived from a systematic literature review , is quite comprehensive. Particularly compared to the rather brief one or two introductory sentences that are often found at the beginning of a literature review section in a standard academic paper. The introduction to the literature review chapter in a thesis or dissertation again adheres to different standards.

Here’s a structured breakdown based on length and the necessary information:

Academic literature review paper

The introduction of an academic literature review paper, which does not rely on empirical data, often necessitates a more extensive introduction than the brief literature review introductions typically found in empirical papers. It should encompass:

• The research problem: Clearly articulate the problem or question that your literature review aims to address.
• The research gap: Highlight the existing gaps, limitations, or unresolved aspects within the current body of literature related to the research problem.
• The research relevance: Explain why the chosen research problem and its subsequent investigation through a literature review are significant and relevant in your academic field.
• The literature review method: If applicable, describe the methodology employed in your literature review, especially if it is a systematic review or follows a specific research framework.
• The main findings or insights of the literature review: Summarize the key discoveries, insights, or trends that have emerged from your comprehensive review of the literature.
• The main argument of the literature review: Conclude the introduction by outlining the primary argument or statement that your literature review will substantiate, linking it to the research problem and relevance you’ve established.
• Preview of the literature review’s structure: Offer a glimpse into the organization of the literature review paper, acting as a guide for the reader. This overview outlines the subsequent sections of the paper and provides an understanding of what to anticipate.

By addressing these elements, your introduction will provide a clear and structured overview of what readers can expect in your literature review paper.

Regular literature review section in an academic article or essay

Most academic articles or essays incorporate regular literature review sections, often placed after the introduction. These sections serve to establish a scholarly basis for the research or discussion within the paper.

In a standard 8000-word journal article, the literature review section typically spans between 750 and 1250 words. The first few sentences or the first paragraph within this section often serve as an introduction. It should encompass:

• An introduction to the topic: When delving into the academic literature on a specific topic, it’s important to provide a smooth transition that aids the reader in comprehending why certain aspects will be discussed within your literature review.
• The core argument: While literature review sections primarily synthesize the work of other scholars, they should consistently connect to your central argument. This central argument serves as the crux of your message or the key takeaway you want your readers to retain. By positioning it at the outset of the literature review section and systematically substantiating it with evidence, you not only enhance reader comprehension but also elevate overall readability. This primary argument can typically be distilled into 1-2 succinct sentences.

In some cases, you might include:

• Methodology: Details about the methodology used, but only if your literature review employed a specialized method. If your approach involved a broader overview without a systematic methodology, you can omit this section, thereby conserving word count.

By addressing these elements, your introduction will effectively integrate your literature review into the broader context of your academic paper or essay. This will, in turn, assist your reader in seamlessly following your overarching line of argumentation.

Introduction to a literature review chapter in thesis or dissertation

The literature review typically constitutes a distinct chapter within a thesis or dissertation. Often, it is Chapter 2 of a thesis or dissertation.

Some students choose to incorporate a brief introductory section at the beginning of each chapter, including the literature review chapter. Alternatively, others opt to seamlessly integrate the introduction into the initial sentences of the literature review itself. Both approaches are acceptable, provided that you incorporate the following elements:

• Purpose of the literature review and its relevance to the thesis/dissertation research: Explain the broader objectives of the literature review within the context of your research and how it contributes to your thesis or dissertation. Essentially, you’re telling the reader why this literature review is important and how it fits into the larger scope of your academic work.
• Primary argument: Succinctly communicate what you aim to prove, explain, or explore through the review of existing literature. This statement helps guide the reader’s understanding of the review’s purpose and what to expect from it.
• Preview of the literature review’s content: Provide a brief overview of the topics or themes that your literature review will cover. It’s like a roadmap for the reader, outlining the main areas of focus within the review. This preview can help the reader anticipate the structure and organization of your literature review.
• Methodology: If your literature review involved a specific research method, such as a systematic review or meta-analysis, you should briefly describe that methodology. However, this is not always necessary, especially if your literature review is more of a narrative synthesis without a distinct research method.

By addressing these elements, your introduction will empower your literature review to play a pivotal role in your thesis or dissertation research. It will accomplish this by integrating your research into the broader academic literature and providing a solid theoretical foundation for your work.

Comprehending the art of crafting your own literature review introduction becomes significantly more accessible when you have concrete examples to examine. Here, you will find several examples that meet, or in most cases, adhere to the criteria described earlier.

Example 1: An effective introduction for an academic literature review paper

To begin, let’s delve into the introduction of an academic literature review paper. We will examine the paper “How does culture influence innovation? A systematic literature review”, which was published in 2018 in the journal Management Decision.

The entire introduction spans 611 words and is divided into five paragraphs. In this introduction, the authors accomplish the following:

• In the first paragraph, the authors introduce the broader topic of the literature review, which focuses on innovation and its significance in the context of economic competition. They underscore the importance of this topic, highlighting its relevance for both researchers and policymakers.
• In the second paragraph, the authors narrow down their focus to emphasize the specific role of culture in relation to innovation.
• In the third paragraph, the authors identify research gaps, noting that existing studies are often fragmented and disconnected. They then emphasize the value of conducting a systematic literature review to enhance our understanding of the topic.
• In the fourth paragraph, the authors introduce their specific objectives and explain how their insights can benefit other researchers and business practitioners.
• In the fifth and final paragraph, the authors provide an overview of the paper’s organization and structure.

In summary, this introduction stands as a solid example. While the authors deviate from previewing their key findings (which is a common practice at least in the social sciences), they do effectively cover all the other previously mentioned points.

Example 2: An effective introduction to a literature review section in an academic paper

The second example represents a typical academic paper, encompassing not only a literature review section but also empirical data, a case study, and other elements. We will closely examine the introduction to the literature review section in the paper “The environmentalism of the subalterns: a case study of environmental activism in Eastern Kurdistan/Rojhelat”, which was published in 2021 in the journal Local Environment.

The paper begins with a general introduction and then proceeds to the literature review, designated by the authors as their conceptual framework. Of particular interest is the first paragraph of this conceptual framework, comprising 142 words across five sentences:

“ A peripheral and marginalised nationality within a multinational though-Persian dominated Iranian society, the Kurdish people of Iranian Kurdistan (a region referred by the Kurds as Rojhelat/Eastern Kurdi-stan) have since the early twentieth century been subject to multifaceted and systematic discriminatory and exclusionary state policy in Iran. This condition has left a population of 12–15 million Kurds in Iran suffering from structural inequalities, disenfranchisement and deprivation. Mismanagement of Kurdistan’s natural resources and the degradation of its natural environmental are among examples of this disenfranchisement. As asserted by Julian Agyeman (2005), structural inequalities that sustain the domination of political and economic elites often simultaneously result in environmental degradation, injustice and discrimination against subaltern communities. This study argues that the environmental struggle in Eastern Kurdistan can be asserted as a (sub)element of the Kurdish liberation movement in Iran. Conceptually this research is inspired by and has been conducted through the lens of ‘subalternity’ ” ( Hassaniyan, 2021, p. 931 ).

In this first paragraph, the author is doing the following:

• The author contextualises the research
• The author links the research focus to the international literature on structural inequalities
• The author clearly presents the argument of the research
• The author clarifies how the research is inspired by and uses the concept of ‘subalternity’.

Thus, the author successfully introduces the literature review, from which point onward it dives into the main concept (‘subalternity’) of the research, and reviews the literature on socio-economic justice and environmental degradation.

While introductions to a literature review section aren’t always required to offer the same level of study context detail as demonstrated here, this introduction serves as a commendable model for orienting the reader within the literature review. It effectively underscores the literature review’s significance within the context of the study being conducted.

Examples 3-5: Effective introductions to literature review chapters

The introduction to a literature review chapter can vary in length, depending largely on the overall length of the literature review chapter itself. For example, a master’s thesis typically features a more concise literature review, thus necessitating a shorter introduction. In contrast, a Ph.D. thesis, with its more extensive literature review, often includes a more detailed introduction.

Numerous universities offer online repositories where you can access theses and dissertations from previous years, serving as valuable sources of reference. Many of these repositories, however, may require you to log in through your university account. Nevertheless, a few open-access repositories are accessible to anyone, such as the one by the University of Manchester . It’s important to note though that copyright restrictions apply to these resources, just as they would with published papers.

Master’s thesis literature review introduction

The first example is “Benchmarking Asymmetrical Heating Models of Spider Pulsar Companions” by P. Sun, a master’s thesis completed at the University of Manchester on January 9, 2024. The author, P. Sun, introduces the literature review chapter very briefly but effectively:

PhD thesis literature review chapter introduction

The second example is Deep Learning on Semi-Structured Data and its Applications to Video-Game AI, Woof, W. (Author). 31 Dec 2020, a PhD thesis completed at the University of Manchester . In Chapter 2, the author offers a comprehensive introduction to the topic in four paragraphs, with the final paragraph serving as an overview of the chapter’s structure:

PhD thesis literature review introduction

The last example is the doctoral thesis Metacognitive strategies and beliefs: Child correlates and early experiences Chan, K. Y. M. (Author). 31 Dec 2020 . The author clearly conducted a systematic literature review, commencing the review section with a discussion of the methodology and approach employed in locating and analyzing the selected records.

Having absorbed all of this information, let’s recap the essential steps and offer a succinct guide on how to proceed with creating your literature review introduction:

• Contextualize your review : Begin by clearly identifying the academic context in which your literature review resides and determining the necessary information to include.
• Outline your structure : Develop a structured outline for your literature review, highlighting the essential information you plan to incorporate in your introduction.
• Literature review process : Conduct a rigorous literature review, reviewing and analyzing relevant sources.
• Summarize and abstract : After completing the review, synthesize the findings and abstract key insights, trends, and knowledge gaps from the literature.
• Craft the introduction : Write your literature review introduction with meticulous attention to the seamless integration of your review into the larger context of your work. Ensure that your introduction effectively elucidates your rationale for the chosen review topics and the underlying reasons guiding your selection.

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Research Article

Vowel onset measures and their reliability, sensitivity and specificity: A systematic literature review

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Validation, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation Voice Research Laboratory/ Doctor Liang Voice Program, Discipline of Speech Pathology, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Sydney, NSW, Australia

Roles Data curation, Formal analysis, Investigation, Writing – review & editing

Roles Data curation, Formal analysis, Writing – review & editing

Roles Data curation, Writing – review & editing

Affiliation Division of Phoniatrics and Paediatric Audiology at the Department of Otorhinolaryngology Head & Neck Surgery, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany

Roles Data curation

Affiliations Division of Phoniatrics and Paediatric Audiology at the Department of Otorhinolaryngology Head & Neck Surgery, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany, Department of Computer Science, Chair of Computer Science 5, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Bavaria, Germany

Roles Conceptualization, Formal analysis, Investigation, Writing – review & editing

• Antonia Margarita Chacon, 
• Duy Duong Nguyen, 
• John Holik, 
• Michael Döllinger, 
• Tomás Arias-Vergara, 
• Catherine Jeanette Madill

• Published: May 2, 2024
• https://doi.org/10.1371/journal.pone.0301786
• Peer Review
• Reader Comments

To systematically evaluate the evidence for the reliability, sensitivity and specificity of existing measures of vowel-initial voice onset.

A literature search was conducted across electronic databases for published studies (MEDLINE, EMBASE, Scopus, Web of Science, CINAHL, PubMed Central, IEEE Xplore) and grey literature (ProQuest for unpublished dissertations) measuring vowel onset. Eligibility criteria included research of any study design type or context focused on measuring human voice onset on an initial vowel. Two independent reviewers were involved at each stage of title and abstract screening, data extraction and analysis. Data extracted included measures used, their reliability, sensitivity and specificity. Risk of bias and certainty of evidence was assessed using GRADE as the data of interest was extracted.

The search retrieved 6,983 records. Titles and abstracts were screened against the inclusion criteria by two independent reviewers, with a third reviewer responsible for conflict resolution. Thirty-five papers were included in the review, which identified five categories of voice onset measurement: auditory perceptual, acoustic, aerodynamic, physiological and visual imaging. Reliability was explored in 14 papers with varied reliability ratings, while sensitivity was rarely assessed, and no assessment of specificity was conducted across any of the included records. Certainty of evidence ranged from very low to moderate with high variability in methodology and voice onset measures used.

Conclusions

A range of vowel-initial voice onset measurements have been applied throughout the literature, however, there is a lack of evidence regarding their sensitivity, specificity and reliability in the detection and discrimination of voice onset types. Heterogeneity in study populations and methods used preclude conclusions on the most valid measures. There is a clear need for standardisation of research methodology, and for future studies to examine the practicality of these measures in research and clinical settings.

Citation: Chacon AM, Nguyen DD, Holik J, Döllinger M, Arias-Vergara T, Madill CJ (2024) Vowel onset measures and their reliability, sensitivity and specificity: A systematic literature review. PLoS ONE 19(5): e0301786. https://doi.org/10.1371/journal.pone.0301786

Editor: Li-Hsin Ning, National Taiwan Normal University, TAIWAN

Received: August 29, 2023; Accepted: March 21, 2024; Published: May 2, 2024

Copyright: © 2024 Chacon et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: Contributions by MD were supported by Deutsche Forschungsgemeinschaft (DFG) under grant no. DO1247/8-2. Contributions by TA were supported by Deutsche Forschungsgemeinschaft (DFG) under grant no. SCHU3441/3-2. Contributions by AC, DN and JH were supported by the Doctor Liang Voice Program at The University of Sydney. The funders had no role in study design, data collection and analysis, decision to publish, nor preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Measures of voicing control provide critical insight into a myriad of voice diagnoses across the lifespan. Voice disorders are highly prevalent, with an estimated one in thirteen adults experiencing a voice disorder each year [ 1 ]. Early and accurate diagnosis are essential to optimise patients’ vocal health outcomes. Traditionally, voice assessment and the evaluation of voice rehabilitative outcomes have focused upon voice quality [ 2 , 3 ] and patient-reported outcomes [ 4 ] as measures of voice function and efficiency. This assessment proforma typically involves the collection of a patient’s case history information, acoustic voice assessment and auditory perceptual judgement of the patient’s voice quality. Ideally, these tasks are also supplemented by laryngostroboscopic and aerodynamic assessment [ 5 , 6 ]. Most current voice assessment methods prioritise steady-state phonation with little, if any focus placed upon the initiation of voicing. Voice onset predicts the voice function that follows and as such, has been increasingly suggested as an effective means of assessing one’s voice, providing predictive information about phonation type, facilitating voice disorder diagnosis and determining one’s response to treatment [ 7 – 10 ].

Voice onset refers to the span of time between the release of a sound and the onset of voicing and involves several physiological processes. The onset of voice begins with transglottal airflow from the lungs bypassing the larynx and the start of vocal fold adduction. Small-amplitude, irregular vibration occurs at the edges of the vocal folds bordering the open glottis. Following the first instance of medial vocal fold contact, the amplitude of these vibrations grows, and steady-state oscillations are established [ 11 , 12 ]. The various physiological components involved in the onset of voice introduce many different means of voice onset measurement. There is also the compounding issue of differing types of voice onset. These are most commonly referred to as soft, breathy and hard, which are discernible to varying degrees depending on the measurement used.

There are two types of voice onset; one occurs after the release of a stop consonant and the other involves vowel phonation without a preceding consonant. Measures of voice onset which focus on the interval between the initial burst of a stop consonant and the voicing onset of the following vowel, e.g., ‘Voice Onset Time’ (VOT) [ 13 ], have been studied widely across populations and health statuses for many decades. The seminal papers in the voice onset literature typically relate to these such contexts of voice onset [ 14 – 18 ], as do most papers within the voice onset literature [ 12 ], with definitions of vowel-initial voice onset often being less clear. The onset of voicing which occurs when a vowel follows a consonant (CV), versus vowel-initial contexts of voicing varies considerably from a measurement perspective. CV measurement requires the ability to detect and differentiate between a consonant and vowel sound before analysing the vowel onset production, while vowel-initial contexts involve detection and measurement from the very start of voicing. Vowel-initial voice onset measurement is more clinically relevant than the measurement of CV productions, as vowel production is one of the standardised tasks performed in voice assessment [ 19 – 21 ]. It also allows for an indication of a patient’s voice production without the articulatory influences which are present in consonant-initial contexts [ 22 ]. Furthermore, the classification of voice onset types has been based primarily on vowel-centric tasks, and not upon vocal productions commencing with a consonant sound [ 7 , 23 ], and yet, vowel-initial voice onset has been researched to a lesser extent than CV voicing. As such, exploring the current state of the literature for specifically vowel-initial voicing onsets has been selected as a focus for this review.

The means through which voice onset has been measured across the existing evidence base is highly variable and has evolved with technological advances over time. Researchers measure voice onset through a range of measurement types, such as auditory perceptual measures, which involve making a judgement about the properties of a sound [ 23 – 25 ]; aerodynamic measures, such as phonatory airflow, volume and pressure [ 26 – 28 ]; physiologically, which monitors the physiological muscle movement associated with voice onset [ 11 , 29 , 30 ]; acoustically, which examines voice signal characteristics related to speech and voice production [ 12 , 31 , 32 ]; visually, through high-speed laryngoscopic examination of the vocal fold vibration associated with voice onset production [ 33 – 35 ], or through a combination of these [ 36 – 38 ]. Each of these methods of voice onset measurement present their own respective strengths and weaknesses, pertaining to the ability of each measure to reflect phonatory function or account for speaker variability, the reliability, sensitivity and specificity of the resulting measurement values, and factors associated with specific equipment requirements, training or skill-level in performing each measurement type. Nonetheless, no literature yet exists which has synthesised and consolidated the measures of voice onset which have been investigated, which are the most reliable, specific and sensitive in identifying or differentiating voice onset types, the contexts in which these measures may best be used, nor established a common language amongst voice onset types and the implications of these upon vocal function. It is imperative that these research gaps be filled so that valid clinical measures of voice onset can be established, which, in turn, can facilitate the inclusion of vowel onset measurement as part of the standardised clinical voice assessment proforma. The aim of this systematic review is to evaluate the evidence for sensitivity, specificity and reliability of vowel-initial voice onset measures, with the authors hypothesizing that high reliability, sensitivity and specificity ratings will indicate the most effective measures of vowel onset. To this end, the proposed systematic review will answer the following question: What are the methods of assessing vowel-initial voice onset and the evidence for their reliability, sensitivity and specificity?

Protocol and registration

This retrospective systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [ 39 ]. The protocol was registered through the PROSPERO International Prospective Register for Systematic Reviews (registration number CRD42021266384) and is provided in S1 File . The completed PRISMA 2020 checklist is provided in S1 Checklist .

Information sources

Databases searched were MEDLINE via OVID, EMBASE via OVID, Scopus, Web of Science, IEEE Xplore, CINAHL and PubMed Central. Grey literature was also searched through ProQuest to capture unpublished dissertations.

Search strategy

The initial search was conducted by AC in August 2021 and limited to articles published after January 1900. The search strategy was initially determined through discussions between four authors (AC, CM, MD, DN). The first author also conducted an updated search in December 2022 and May 2023 to capture any further articles of relevance ahead of publication.

The search string consisted of terms relating to three ‘concept areas’: voice onset, voice onset measures and evidence for measures of voice onset. Within the selected concept areas, we developed a list of synonyms and/or specific terms relevant to our search scope. The terms associated with each concept area were searched against the other concept word lists to achieve literature saturation of all relevant articles. The search strategies and Boolean operators applied to the MEDLINE, EMBASE, Scopus, Web of Science, IEEE Xplore, CINAHL, PubMed Central and ProQuest databases are provided in S2 File .

Inclusion criteria

The scope of this literature review was the onset of vowel phonation without a preceding consonant. Studies and unpublished works were included if they were written in English, related to measures of human voice onset and were published after 1900. Nil study design limits were enforced, nor were specific settings of interest; research occurring in both laboratory and clinical settings were included. Articles were excluded if they related to the onset of artificial or computerised tones, examined voice onset in vowels following the production of a consonant sound (i.e., Voice Onset Time) and/or were not written in the English language.

Study records

The database searches retrieved 6,983 records. These records were uploaded to the Covidence platform ( www.covidence.org ) to manage data, facilitate collaboration and document the review process over the course of the study.

Covidence identified 550 duplicates which were then removed for a total of 6,433 records. Titles and abstracts were screened against the inclusion criteria by two independent reviewers (any combination of MD, AC, DN, JH and TA). Any disagreements which arose between the reviewers at each stage of the selection process were resolved through the involvement of a third reviewer. Five thousand, nine hundred and twenty-two records were excluded based on titles and abstracts, with a further 11 studies being excluded as their papers could not be retrieved. Full texts of the remaining 500 records were assessed in detail against the inclusion criteria by two independent reviewers (any combination of DN, AC, MD, TA, JH and CM). Articles that did not meet the study criteria were removed, with reasons for exclusion being recorded. Four hundred and seventy-two papers were excluded from this process. For the purposes of literature saturation, a further hand search of the remaining articles’ citation lists was conducted (AC). Following a further process of title/abstract screening (MD, AC, DN, JH and TA), full text review and exclusion of inappropriate studies (AC, DN, MD, JH and TA), an additional seven studies were included.

An updated review of the literature was conducted in December 2022 and May 2023. The processes of title/abstract screening (AC, DN, JH), full text review and exclusion of inappropriate studies (AC, DN, JH), were again completed. The December 2022 search found nil further studies appropriate for inclusion, while the search conducted in May 2023 identified a further two studies. The final systematic review included 35 studies. A visual representation of this process is shown in Fig 1 , formatted according to the PRISMA 2020 statement [ 39 ].

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Data extraction and data items

Data was extracted from the included papers by all members of the research team. The data extraction process involved each team member reading the paper in its entirety, before extracting all information of relevance into the data extraction table. A simplified version of this table is presented in S3 File and the OSF Home Repository (DOI 10.17605/OSF.IO/N65SX ). Quantitative synthesis and meta-analyses were not completed owing to the heterogeneity of data and methodologies across studies. Rather, studies were grouped according to their voice onset measurement category (see Table 1 ). Following the study groupings, the data extracted from all studies across each measurement category was closely examined to identify key relationships and discrepancies across and between papers and categories. This informed the key research findings which are summarised in the Results section.

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Evaluation of certainty of evidence and risk of bias

The certainty of the included evidence was assessed through the Grading of Recommendations Assessment, Development and Evaluation (GRADE) working group methodology [ 40 ]. This involved each reviewer examining the quality of evidence through the domains of risk of bias, consistency, precision, directness and publication bias. This was particularly facilitated using the GRADE Handbook [ 41 ], which was used by team members to inform their assessment and provide a consistent evaluation across raters. Following this evaluation, it was determined whether the quality of the research could be deemed as high (i.e. very unlikely that further research will change our confidence in the estimate of effect), moderate (i.e. likely that further research will have an impact on our confidence in the estimate of effect and may change the estimate), low (i.e. very likely that further research will have an important impact on our confidence in the estimate of effect and is likely to change the estimate), or very low (i.e. very uncertain about the estimate of effect). The GRADEpro app was used to facilitate this process and ensure that the abovementioned terms were informed by a consistent, systematic process [ 42 – 44 ].

Process of identifying studies

The PRISMA flowchart in Fig 1 outlines the processes undertaken to collect and review the study records. Thirty-five records were identified as meeting the inclusion criteria for the review. Twenty-three studies involved visual imaging, 19 studies conducted acoustic analysis, 11 used physiological measures, seven studies involved auditory perceptual analysis, and four included aerodynamic analysis.

Study design

Of the 35 studies included, 26 used a cross-sectional design, six were validation studies, two were review papers with single or multiple case examples and one was a cohort study. No study used a randomised controlled trial design.

Study population characteristics

Table 1 presents an overview of each record included in the review, summarising study setting, participant characteristics, category of measurement and evidence certainty. It should be noted that while some studies specified the setting in which their research took place, most settings could only be extrapolated from the study methodology. Studies which used data from only vocally healthy, normophonic speakers (i.e., non-patients) were classified as taking place in a laboratory setting. Studies which involved patients with some form of voice disorder diagnosis were classified as ’clinical’. However, only one study explicitly stated that patients were recruited directly from a voice clinical setting [ 34 ]. Table 2 offers a summary of study population characteristics across the collective paper set, including sample size, age, gender, vocal health status and setting.

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Voice onset types

A definition of voice onset was provided in 25 of the 35 studies (see S1 Checklist ). Ten of these provided definitions of the specific voice onset measures used throughout the study (e.g., Vocal Attack Time), and 15 included the concept of voice onset being the period between the first adductory movement of the vocal folds and steady-state vibration. Twenty-one studies specifically examined different types of voice onset, namely being breathy (also referred to as ‘aspirate’), normal (also referred to as ‘comfortable’, ‘soft’, ‘easy’ and ‘modal’) and hard (also referred to as ‘glottal’, ‘pressed’ and ‘hard/glottal attack’) voice onset types.

Whilst these are auditory perceptual classifications, not all studies compared or validated their instrumental measures with independently-rated auditory perceptual judgements, despite using voice onset type as a classification or identifier. Only three studies of the review set compared their instrumental measure to perceptual judgements. As auditory perceptual judgement of voice is considered the ‘gold standard’ of voice assessment [ 61 ], it is noteworthy that few studies used comparisons to auditory perceptual judgements to validate the measure being investigated.

Across the 35 studies, a wide range of voice onset measures were explored. Amongst these, some focused on a singular measure (e.g., laryngeal reaction time) whilst others examined one measure using several means of instrumentation, for example, Vocal Attack Time (VAT), which is measured using the vocal acoustic and glottographic signals. Other studies examined or compared several measures of voice onset. Overall, 39 different measures of voice onset were identified across the collective set. Our team mutually agreed that the best means of synthesising and presenting this heterogeneous data set was through grouping the studies according to their measurement approach. As such, the following categories of measurement were identified; acoustic, aerodynamic, auditory-perceptual analysis, physiological measures and visual imaging. In any case where a given study explored more than one category of measurement, it was included across all relevant categories. The collective findings across each of these measurement categories are outlined in the sections below.

Voice onset measures

In total, there were 39 voice onset measures across the collective dataset. These are presented with their definitions in Table 3 . These measures were developed and investigated using different methods of analysis, which are described in the following text.

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Categories of voice onset measurement

A) auditory perceptual analysis..

Auditory perceptual analysis involves a listener making an auditory judgement about the properties of a sound. In the case of voice onset studies, this judgement often relates to the type of onset produced. Seven of the 35 included studies involved auditory-perceptual analysis. All seven studies involved perceptual ratings of phonation onset type, ranging from soft to hard [ 23 – 25 , 37 ], breathy to ‘German’ (a glottal plosive occurring in German classical singing) [ 36 ] and breathy to hard/ pressed [ 7 , 38 ]. For four of the seven studies [ 7 , 36 – 38 ], the auditory perceptual rating of samples was used only as a form of correlation to an instrumental measure of voice onset. This also served as confirmation that the participants had produced the onset types correctly before proceeding with other voice onset measurements; with 67% concordance between the attempted phonation type and rater in Shiba and Chhetri’s study, 68% agreement reported in Cooke et al.’s paper, 80% of samples being correctly identified in Freeman et al.’s study and 100% agreement on attack types in Koike’s study. Each of the studies explored different measures of voice onset, with three studies examining auditory perceptual judgements of voice onset as a voice onset measure in and of itself. Peters, Boves and Van Dielen, Maryn and Poncelet and Simon and Maryn’s papers focused on auditory perceptual judgement of voice onset as a standalone voice onset measure, with Maryn and Poncelet and Simon and Maryn concluding that there was considerable variability both between and within raters regarding the perception of voice onset type. Meanwhile, Peters reported moderately high reliability of ratings (r 1.1 = 0.74).

Automation of voice onset measurement was involved in four of the seven studies, and only in the processing and data generation stages for measures unrelated to auditory perceptual analysis. All seven studies performed some form of reliability analysis, which is presented in Table 4 . Two studies conducted both inter- and intra-rater reliability [ 24 , 25 ], with the remainder only exploring inter-rater reliability. Percentage agreement [ 7 , 36 – 38 ], product-moment correlations [ 23 ], the intraclass correlation coefficient [ 24 , 25 ] and Cohen’s kappa [ 25 ] were the statistical measures used to calculate reliability. None of the seven papers explored sensitivity nor specificity of data obtained.

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Collectively, the studies presented conflicting findings. Whilst Freeman et al., Peters et al. and Koike’s papers suggested listeners could discriminate well between onset types, Cooke et al., Shiba and Chhetri, Maryn and Poncelet and Simon and Maryn’s papers indicated that auditory perceptual judgement of voice onset type can be unreliable both within- and between-raters. Six of the studies reflect the lowest GRADE level of evidence with a rating of ‘very low’ evidence certainty and one with a rating of ‘low’ certainty of evidence. This low quality of research evidence combined with the variability in the findings of these studies calls into question the value of auditory perceptual judgements as the most accurate and reliable means of assessing voice onset in clinical contexts. A summary of data extracted from these auditory perceptual studies is provided in Table 5 .

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b) Acoustic analysis.

Acoustic analysis involves examining the recorded voice signal characteristics related to speech and voice production. Amongst the studies included, 19 utilised acoustic analysis in their voice onset measurement procedures. A wide range of acoustic voice onset measures were explored, as summarised in Table 6 , inclusive of Vocal Rise Time (VRT), the first peak of the acoustic derivative waveform (ADW1) and Laryngeal Reaction Time (LRT). Papers exploring most acoustically derived measures of voice onset did not typically provide numeric data for each onset type. Rather, these presented data ranging from descriptions of onset type differences, such as vibration and amplitude patterns, often in the absence of complete data reporting (for example, [ 30 ]), to small datasets regarding a new or uncommonly used voice onset measure. A common feature across all presented acoustic measures was the limited utility of applying these measures in clinical contexts, with many requiring specialised software or processes which would be expensive and/or impractical to complete during a clinical session.

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No specifications of voice recording equipment were provided for model number nor brand for six studies and two studies provided no specification whatsoever of device used. An integrated microphone (I.e., a microphone integrated into a stroboscopy or similar system) was used in two studies, and a further three studies used an audiotape recorder. Only one of the devices was used across more than one study (RadioShack 33–3012 head-mounted microphone), however all three studies in which it was used involved a similar research team. Some form of automation was involved in the methodology of 14 of the included acoustic analysis studies, and usually this was across both the processing and data generation stages using software platforms and mathematical algorithms. Three of the included papers used auditory perceptual analysis as a means of validating the instrumental measures used [ 36 – 38 ].

Only seven studies reported reliability assessment of acoustic analysis, of which two explored both inter- and intra-rater reliability [ 12 , 35 ] and five explored only inter-rater reliability [ 23 , 36 – 38 , 54 ]. The following statistical methods were used to determine reliability across the studies: Pearson product-moment correlation [ 12 , 23 , 51 , 54 – 56 ], percentage agreement [ 36 , 37 ] and multivariate tests [ 35 ]. One of the studies that used acoustic measurements for voice onset reported sensitivity analysis [ 35 ], with none conducting an analysis on specificity.

In summary, the included acoustic analysis studies reflected low evidence certainty, with outcomes from the GRADE Certainty Assessment yielding a ’very low’ rating for 14 studies, and a rating of ’low’ for the remaining five. While a large proportion of the reviewed studies involved acoustic analysis measures, there is evidently a vast range of acoustic analysis measures being used which prevents an in-depth understanding of any given measure. The acoustic analysis findings overall cannot be interpreted with high levels of confidence, nor are they of sufficient quality to inform the selection of the most reliable, sensitive, and specific acoustic voice onset measures for clinical practice.

c) Aerodynamic analysis.

Aerodynamic analysis refers to the measurement of phonatory airflow, volume, pressure and combined measures, such as efficiency and resistance. Four papers reported airflow measurement information informing some aspect of voice onset. The specific airflow measures explored across these studies included air consumption during the initial 200 milliseconds of different attack types (soft, breathy and hard) [ 37 ], Phonation Threshold Pressure (PTP) [ 27 ], Voice Onset Coordination (VOC) [ 28 ] and vocal onset according to transglottal airflow and intraglottal pressure [ 26 ].

Koike and LeBacq and DeJonckere’s papers similarly focused their studies upon exploring the characteristics of different voice onsets. Koike identified that soft and hard onsets were diametrically opposed across a range of measures, while the breathy onset showed little relation to either, having a ‘distinct character’ that differed completely from soft and hard onset types. LeBacq and DeJonckere namely used their airflow data as part of an intraglottal pressure calculation, while Madill et al.’s study correlated existing voice onset measures, including VOC, with the measure ADW1, concluding that it can be predicted from VOC. In Plant’s exploration of phonation threshold pressure, it was found that for most subjects, increasing airway resistance coincided with increasing threshold pressure.

Devices used for airflow measures were largely consistent, with three of the four studies using a Rothenberg mask or equivalent, and the other paper using a pneumatochograph [ 37 ]. Most of the four papers didn’t involve any automated processes, apart from Madill’s study, which involved some automation only in the data generation phase. Only Koike’s study involved some form of reliability assessment, being inter-rater reliability established through percentage agreement. None of the studies performed an analysis of sensitivity nor specificity. None of the included papers used auditory perceptual ratings to validate the instrumental measures of voice onset used.

Overall, the aerodynamic data presented across these four studies did not contribute significantly to an understanding of the most effective means of assessing voice onset through airflow. Other than Koike and Madill, there is a lack of transparency when it comes to presentation of the aerodynamic voice onset data. These findings should be considered as offering indefinite conclusions pertaining to the value of aerodynamic voice onset measurement, particularly as all four studies were graded as having the lowest certainty of evidence, being ‘very low’ evidence certainty according to the GRADE rating system. A summary of these aerodynamic analysis studies is provided in Table 7 .

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d) Physiological measures.

A range of other instrumental measures that monitor physiological muscle movement have been used to measure voice onset. For the purposes of this review, this specifically relates to electroglottography (EGG) and electromyography (EMG). EGG is a non-invasive technology used to measure the varying degrees of vocal fold contact during voice production, while EMG is a measure of muscular response or activation. Eleven studies explored physiological measures of voice onset. The specific types of voice onset measures examined in these studies included VAT [ 11 , 28 , 29 , 51 , 52 , 55 , 56 ], maximum of the first derivative of the EGG signal [ 27 ] and the interval between the first action potential (as detected by EMG) and the onset of sound [ 37 ].

The three studies of low evidence were largely conducted by the same research group [ 51 , 52 , 56 ], and all explored VAT as a measure of voice onset. However, the research questions posed in each of these studies differed, ranging from determining the fidelity of VAT as a voice onset measure to establishing normative VAT values. Pearson’s correlation coefficient was found to be a suitable fidelity metric (median correlation coefficient of 0.975 for 1033 VAT measures) [ 51 ], with the mean VAT among healthy young adults reported as 1.98ms. Aspirated voice onsets (e.g., the production of ‘hallways’) lead to a greater mean VAT than unaspirated voice onset tasks (e.g., the production of ‘always’) [ 56 ]. All remaining studies were of ‘very low’ evidence certainty; the majority of which also explored VAT.

Devices used across the physiological studies were varied, with three studies providing no specification of equipment. The remaining eight studies included one electromyograph and the remainder a combination of electroglottographs of different brands and models, with only the Glottal Enterprises EG2 and the KayPENTAX Fourcin Laryngograph model 6091 occurring in more than one study (each used in two studies). Six of the included studies involved automation as part of their study methodology for physiological measures, with five of these employing automated processes or algorithms across both the data processing and generation stages and one only using automation for data generation.

Reliability analysis was only performed in one study; Koike, 1967, which conducted inter-rater reliability as determined through percentage agreement (see Table 4 ). Neither sensitivity nor specificity analysis was conducted in any of the papers within this category. Only one of the papers in this set included auditory perceptual analysis to validate the instrumental measures of voice onset used.

Collectively, the studies of the highest GRADE level of evidence examining physiological measures of voice onset use VAT. Despite the greater breadth of research upon VAT than most other voice onset measures, there is a requirement to collect both electroglottographic and acoustic data to attain the VAT value. This, combined with the limited availability of the MATLAB-based program to calculate the measure, the heterogeneity amongst research questions posed in these studies, and the highest evidence rating according to the GRADE rating system as ‘low’ calls into question its clinical utility. A summary of the studies involving physiological analysis is provided in Table 8 .

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e) Visual imaging.

Visual imaging relates to any study whereby a measure of voice onset was based upon still or motion pictures of the larynx. Amongst the 35 included studies, 23 involved visual imaging in their measurement of voice onset. These studies investigated a range of measures related to voice onset, including Phonation Onset Time (POT) [ 38 , 48 , 50 , 59 ], measures of velocity, angle, distance and time associated with voice onset [ 7 ], Voice Initiation Period (VIP) [ 35 , 46 , 50 ] and Glottal Attack Time (GAT) [ 34 ].

Twenty of the 23 studies in this category involved high speed visual imaging, with kymography used in five studies [ 11 , 36 , 38 , 53 , 60 ], rigid laryngoscopy in one [ 7 ] and one employing cine-radiographic techniques, i.e., the recording of laryngeal movements on x-ray film [ 37 ]. Devices used across the visual imaging studies were varied, with the most common device used being the KayPENTAX colour high speed video system and component model 9710, used in five of the 23 studies. Six studies did not specify the device used, and of the remaining studies, 11 used some form of high-speed camera system and the remaining study performed cineradiography. Nineteen studies utilised a software program or mathematical algorithm to automate the processing and/or analysis of data pertaining to vocal fold vibration and glottal characteristics ( Table 9 ).

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Ten studies used reliability assessment in their measurement protocols, involving three which explored both inter- and intra-rater reliability [ 12 , 33 , 35 ], five inter-rater [ 7 , 34 , 36 – 38 ] and two intra-rater reliability assessments [ 49 , 50 ]. The statistical methods used for reliability assessment included Pearson product moment correlations [ 12 , 49 ], Cohen’s kappa [ 33 ], Cronbach alpha [ 50 ], Pearson’s correlation coefficient, general linear model and repeated measures analysis [ 35 ], the Wald 99% confidence interval [ 34 ] and percentage agreement [ 7 , 36 – 38 ]. Most studies did not report any sensitivity assessment, except for one paper [ 35 ]. No studies conducted specificity analysis. Three of the papers which involved visual imaging included auditory perceptual analysis to validate the instrumental measures of voice onset used.

Regarding the GRADE Certainty Assessment, one study was rated as ‘moderate’, two as ‘low’, and 20 as ’very low’ certainty of evidence. The findings of this section prove that the use of equipment (namely laryngoscopy) can introduce further variance in voice onset measures used, with an extensive range of voice onset measures despite the similarities across the visual imaging hardware used.

Automated voice onset measures

In examining the 35 studies, an interesting theme which arose was the increasing use of task automation to obtain voice onset measures in recent years. For the purposes of this review, ‘automation’ refers to any process throughout a study’s methodology which uses a form of computerised software or algorithm to eliminate the manual need to prepare or process data. Only nine studies [ 24 – 27 , 29 , 37 , 51 , 57 , 60 ] were found to involve no automated processes. These studies generally involved a research question focused upon auditory perceptual judgements, reliability or fidelity checking, or presented a descriptive review of a specific voice onset measure based on previous literature, and as such did not involve the analysis of large sets of objective voice onset measurement data. There were four studies which only involved automation in the pre-processing phase [ 23 , 33 , 34 , 38 ], with most using an automated process for both pre-processing and/or voice onset data output. Three studies used automation for data output alone [ 28 , 32 , 49 ]. According to measurement category, those studies which fell within the visual imaging and acoustic categories mainly used automation for processing and data. Across the remaining categories of physiological, aerodynamic and auditory perceptual studies, the automated phases of data analysis tended to vary more greatly.

Across the 26 studies which used automated algorithms, 12 used solely proprietary software or programs to perform automated functions upon their datasets, nine used only customised algorithms or programs, three used a combination of either proprietary and custom software, or used proprietary software with customised algorithms or applications specific to the research project and two were unspecified/unclear. There were several proprietary tools used across multiple studies, with the most common being MATLAB, in seven papers. While certain algorithms and filters were also named and described across studies, a close examination of these is beyond the scope of this paper.

Research quality

The process of data extraction included extracting data pertaining to the conduction of reliability, sensitivity or specificity analysis in any of the 35 studies. It was found that fourteen of the 35 studies conducted some form of reliability analysis while one conducted some form of sensitivity or specificity analysis. According to measurement category, reliability analysis was most commonly conducted in auditory perceptual studies, with all auditory perceptual papers conducting some form of reliability analysis. Reliability analysis was also common in the acoustic and visual imaging categories, with just under 50% of papers in both categories reporting reliability ratings. While 25% of papers in the aerodynamic category involved reliability analysis, this was least common in the physiologic category, with only one of 11 papers reporting reliability. Sensitivity was reported in one paper, which was common to both the acoustic and visual imaging categories. Specificity analysis was not conducted in any measurement category.

Of the papers which included reliability checking, two performed exclusively intra-rater reliability, while seven solely performed inter-rater reliability analysis. Five papers examined both intra- and inter-rater reliability. For intra-rater reliability, the number of samples re-rated for the purposes of reliability ranged from 10% [ 24 , 35 ] through to 36% [ 50 ], with reliability agreement ranging from an ICC value of 0.341 (one rater with poor intra-rater reliability [ 24 ]) to an ICC value of 0.975 [ 12 ]. Of those studies examining inter-rater reliability agreement, the number of samples re-rated varied from 10% [ 35 ] to 100% [ 7 , 23 – 25 , 36 – 38 ]. Inter-rater reliability agreement ranged from an ICC value of 0.145 [ 24 ] to 0.998 [ 54 ].

The metrics used to assess both intra- and inter-rater reliability included the intraclass correlation coefficient [ 23 – 25 ], Pearson product-moment correlations and absolute difference [ 12 , 49 ], Pearson’s correlation coefficient [ 35 , 54 ] and Cohen’s kappa [ 25 , 33 ]. Cronbach’s alpha [ 50 ] was used to determine intra-rater reliability in a single study, while percentage agreement [ 7 , 37 , 38 ], the general linear model and repeated measures of analysis [ 35 ] and the Wald 99% confidence interval [ 34 ] were used only for inter-rater reliability calculations. It should be noted that percentage agreement, as used in Shiba and Chhetri, Freeman et al., Cooke et al. and Koike’s studies should not be used as a standalone statistical measure for inter-rater reliability assessment, as these percentages do not account for concurrence that can be expected by chance, and ultimately does not represent a robust means of determining reliability agreement [ 25 ].

Only one of the 35 included studies conducted sensitivity analysis, with no studies conducting an analysis on specificity. Kunduk [ 35 ] posed a research question specifically related to sensitivity, determining whether the timing characteristics, pattern of adduction, start of vocal fold vibration and number of cycles required for the vocal folds to reach full vibration were sensitive to aging, as measured by the VIP. It found that timing characteristics during the VIP were sensitive to the effects of aging, with all timing variables being higher in the older group (mean age 76 years) than the younger group (mean age 26 years). However, the only measure found to reach a significant difference between the younger (mean = 11 cycles) and older groups (mean = 14 cycles) was the number of vocal fold oscillatory cycles before full length vocal fold vibration was achieved (p = 0.001). Across the remaining 34 studies, a select few made a comment relating to sensitivity when interpreting their results [ 30 , 37 , 47 , 54 , 55 ], however no sensitivity analyses was completed.

While most studies did not report sensitivity nor specificity analysis, 18 of the 35 did seek to use their chosen measure/s of voice onset to differentiate between voice onset types. However, many of these provided an in-text description of what appeared to differ across voice onset types (e.g., how a particular waveform or kymograph varied between breathy and hard onsets), rather than offering numerical cut-off values.

Overall, while the abovementioned papers report reliability outcomes to be of an acceptable level across studies, and VIP to be a sensitive measure of voice onset in detecting age-related differences between patients for the number of vocal fold oscillatory cycles, collectively it is clear that most voice onset measures have not been studied to the level required to be certain of their reliability, sensitivity and specificity.

GRADE evaluation of research quality

All authors used the GRADE system to evaluate research quality. This evaluation was completed immediately following data extraction for each study. Across all papers, the certainty of evidence as evaluated by GRADE ranged from ‘very low’ to ‘moderate’, with 27 of 35 papers falling in the ‘very low’ category, seven papers classed as ‘low’ certainty and one as ‘moderate’. GRADE certainty assessment values were similarly low across all measurement categories, with the single study assessed as moderate evidence certainty being classed within the ‘visual imaging’ category.

Acoustic analysis studies ranged from very low to low, with 14 categorised as ‘very low’ and five as ‘low’ certainty of evidence. Those four studies exploring aerodynamic analysis were all classed as ‘very low’ certainty of evidence, as was the case for six of the auditory perceptual papers, with one being classed as ‘low’ evidence certainty. The eleven physiological papers ranged from ‘very low’ to ‘low’ evidence certainty, with eight being ‘very low’ and three falling in the ‘low’ certainty of evidence category. Visual imaging was the voice onset measurement category with the largest number of papers, ranging from ‘very low’ to ‘moderate’ certainty of evidence. Amongst these papers, 19 were rated as ’very low’, three as ‘low’ and a single paper was deemed to have ‘moderate’ certainty of evidence.

Summary of main findings

Across the 35 studies included in this systematic review, all methods of voice onset measurement examined could be classified into one of five categories: auditory perceptual, acoustic, aerodynamic, physiological measures and visual imaging. These studies were evaluated as showing low level of evidence, ranging from very low to moderate certainty of evidence according to the GRADE rating system. Collectively, we found that the reviewed literature presents high variability in vowel onset measures, methodology and automated processes applied, with a lack of robust, high-quality data for any given measure of vowel onset. The voice onset measure explored by the greatest number of studies was VAT, having been examined in seven studies with the highest quality paper reflecting a GRADE rating of low-quality evidence. The paper with the highest evidence rating according to the GRADE system was of moderate evidence certainty [ 49 ], with all other papers being rated as low or very low. Overall, none of the 35 papers in question present high quality research evidence, with a clear paucity of studies examining measures of voice onset in a clinical context. As such, the present literature findings prevent a conclusion of which measures of voice onset would yield the most reliable results with satisfactory sensitivity and specificity to be used in clinical practice.

Heterogeneity in dataset

The collective data preclude a conclusion pertaining to the most reliable, sensitive and specific measures of voice onset for a variety of reasons. Firstly, across the 35 papers, there is great heterogeneity in the study populations used. There is variability in sample size, ranging from 1 to 112 participants per study and in ages explored, with those studies which report the age of their participants extending from ages eight to 87 years. A further source of variability is the genders included across the studies, with those which report the gender of their participants having an exclusively female or male population or a combination of both. Furthermore, the inclusion of a control or dysphonic group within each paper varies greatly. While most papers only examined normophonic participants, seven involved either an exclusively voice-disordered population or a matched group of participants with voice disorders, with diagnoses ranging from neurological disorders (spasmodic dysphonia) to vocal hyperfunction (vocal nodules) and malignant conditions (laryngeal cancer). Collectively, this extensive scope of participant demographics in each study population prevents both the generalisation of these findings to a larger population and the ability to draw an informed and cohesive conclusion pertaining to the reliability, sensitivity and specificity of the voice onset measures explored.

A further source of heterogeneity across the studies is found in the measurement methods used, with studies exploring either auditory perceptual, acoustic, aerodynamic, physiological or visual imaging-based measurement types, or in 18 studies, a combination of these. Across the 35 studies there are 39 different measures of voice onset used. Even in the case of VAT, the most explored voice onset measure in the dataset, there is variability in how this measure is collected, with a difference in approach evident across research groups. This variance in measurement methods over time can be attributed to technological advances. Many vowel-initial measures of voice onset may never reach the stage of becoming clinically practicable as new measures, based on updated technology and approaches, are constantly being developed before existing measures are sufficiently researched and applied to clinical contexts of voice assessment.

The automation of processes throughout the methodology of studies introduces a further source of variation in the voice onset literature. Automation is applied throughout the dataset in the stages of data processing, data generation or a combination of the two, with 27 of the 35 studies using automation in some capacity throughout their methodology. With a vast variety of algorithms and software platforms employed across these studies and the differing stages where these automated processes are applied, it is evident that automation introduces furthermore heterogeneity of measurement across the vowel-initial voice onset literature.

There are several potential sources of this heterogeneity. Voice onset is a complicated measure, such that currently there appears to be no single measure able to quantify it satisfactorily. This may have led to ‘exploratory’ studies in the absence of a theoretical model of voice onset, which introduces variation in the way vowel onset is measured and explored. Other sources can be attributed to the array of robust research indicators which are presently lacking across the vowel onset evidence base. The current evidence lacks well-designed studies which include a pre-calculated sample size, random sampling of the study population, theoretical models and reliability, sensitivity and specificity ratings for outcome measures of interest, reasonable rationales for vocal tasks used, voice disorder classification criteria, focal voice disorder populations (i.e., currently there are mixed population groups, such as functional and organic voice disorder types) and standardised voice onset measurement protocols. This range of factors can likely be attributed to the extensive variation between each of the studies which make up the collective set.

This heterogeneity in turn, limits interpretation and generalisability of the presented data. Across the study set, limited and underestimated sample sizes are highly prevalent, with all studies lacking a pre-calculated sample size with sufficient statistical power. This limits the ability to meaningfully interpret any data and apply this to larger populations. The lack of standardised protocols and reliability analyses across the reviewed studies is another contributing factor, which results in issues with the data reported and difficulty in interpreting this. Finally, the inconsistencies in methodology, outcome measures, measurement techniques and results across studies make it exceedingly difficult to draw significant trends and conclusions.

Collectively, there is great variability in the measurement of the voice onset phenomenon from methodological approach through to selected voice onset measure, leading to a vast array of data that can’t easily be replicated, interpreted nor synthesised. This heterogeneity prevents us from ascertaining the clinical utility of each respective measure and as such, disallows us from forming any generalisations pertaining to clinically valid measures of vowel onset. The diversity in methods and approaches highlights the lack of a commonly accepted standard when performing voice onset analysis, which further limits the opportunity to appreciate how voice onset could best, most reliably, sensitively and specifically be applied in a clinical context.

Voice onset definitions

An added limitation of the study findings is grounded in the lack of accepted definitions pertaining to voice onset in vowel-initial contexts. While most studies provided some form of voice onset definition, there was considerable variation between these; with ten defining only the specific voice onset measure/s examined in their study and a further ten papers describing voice onset according to a clear and detailed definition which accounted for the range of physiological processes involved. Of the papers which did not specify the meaning of voice onset, these often reported providing instruction, training and/or modelling to study participants which is not detailed in each paper (for example, [ 36 ]). Training of subjects requires perceptual judgement of voice onset by trainers and speakers to perform the voice onset. Therefore, the lack of independent verification of perceptual features present in the samples where auditory perceptual ratings were not used is problematic. This lack of reporting also limits the opportunity for replicability and consistency between studies. Without the provision of clear and explicit definitions of vowel-initial voice onset across the literature, it is difficult to establish if the phenomenon being measured is in fact voice onset. Given that the definition of voice onset informs the methodology and nature of research conducted across each study, this discrepancy across the collective dataset is a clear contributing factor to the heterogeneity of study design and outcomes.

The issue of ambiguity surrounding what specifically is being measured as voice onset is further compounded by the lack of correlation with auditory perceptual judgements throughout the collective group. With only three of the papers correlating their instrumental measures of voice onset with a perceptual judgement of onset type, most papers are neglecting the gold standard of voice assessment and in so doing, bringing into question the validity of their chosen measures of vowel-initial voice onset.

Quality of evidence

The GRADE findings of this review evidenced that the quality of papers throughout the vowel-initial voice onset literature is low, informed largely by the research design and small sample size of all studies examined. Amongst these papers there was a low incidence of reliability assessments to ascertain the reproducibility of research findings, with some form of reliability assessment occurring in only 14 of the 35 papers. Across these papers, these ratings tended to be quite variable, including instances of low reliability reported. This may have resulted from factors pertaining to the raters themselves (i.e., variation in clinical experience, skill set and training in use of the measurement tool) but is most likely attributable to elements associated with research quality, such as study design, sample size and sampling methods. A cross-sectional study is typically less reliable than prospective or cohort studies, small sample sizes yield less reliable results than studies involving greater participant numbers and convenience sampling is generally less reliable than random sampling. With cross-sectional studies being the most common study design and the use of small sample sizes attained through convenience sampling across the 35 papers, the overall low quality of the collective paper set elucidates some causative factors behind the low and variable reliability results reported in this review.

Compared to reliability analysis, even lower rates of sensitivity assessment were performed with only a single study reporting some form of sensitivity analysis, and nil studies were found to analyse specificity. Almost none of the reviewed studies used voice onset measures to discriminate disordered from non-disordered speakers. Furthermore, voice onset measures were not used as an outcome to detect participants’ vocal condition. These factors help to account for the lack of discrimination analyses conducted across the studies.

Strengths and limitations

The papers included in the systematic review covered all types of relevant literature available at the time of the study, featuring a comprehensive search strategy including both published papers and grey literature sources. Updated searches were conducted in December 2022 and May 2023 to ensure all recently published articles of interest were considered for review. Limitations of the study approach include only examining literature published in the English language i.e., excluding non-English sources, and not performing a further citation search of the two studies added to the dataset from the final updated literature search, which may have potentially sourced further studies of relevance. A lack of quantitative data and a high level of heterogeneity between the studies prevented the conduction of a quantitative analysis of the collective study findings. The dearth of data conducted beyond a laboratory-based setting also made it difficult to determine which measures of voice onset may be most practical for application in clinical contexts. As such, we are unable to develop well-informed recommendations and conclusions pertaining to how voice onset may be most effectively measured in patient scenarios, as these conclusions would not be supported by research we would describe as reliable, sensitive nor specific.

Comparison with other studies

Nil other review studies have been conducted into vowel-initial voice onset measurement to enable a direct comparison with the existing literature, however, several studies have recognised that the existing pool of voice onset measurement literature presents a heterogeneous set of data and low level of evidence methodologies. For example, Patel [ 49 ] reported that studies investigating the onset of phonation examine small cohorts of vocally healthy adults and have utilised different waveform types, which yields variable findings. Likewise, Petermann and colleagues [ 62 ] recognised that the present literature involves different approaches to measuring even the same voice onset measure, with no standardised processes in place and wide inter- and intrasubject variability, which complicates the cross-study comparison of results. Maryn and Poncelet [ 24 ] also recognised the failings of the existing voice onset literature in examining or developing a range of quantitative, objective voice onset measures, without any application to clinical voice assessment protocols nor patient-centric contexts.

Clinical implications

The lack of an accepted standard pertaining to vowel-initial voice onset measurement in clinical contexts is directly evidenced in the range of clinical voice assessment proformas which lack an assessment of this feature. Despite the utility of vowel-initial voice onset in providing predictive information pertaining to the voice function that follows, the plethora of studies relating to vowel-initial voice onset measures have proved trivial in bridging the gap between theory and practice; failing to identify a single form of measurement which is proven to yield reliable, sensitive and specific results which can be applied to clinical voice patient contexts. Until such a measurement tool can be identified and researched to prove its utility as a clinically valid measure, it seems that clinical voice assessment and the standardisation of voice assessment tasks will continue to be limited by the current gaps in the voice onset literature.

Implications for research and future studies

Further, high quality research is clearly needed in the vowel-initial voice onset measurement space, preferably, within the next five to ten years. These papers would ideally involve a comparison of voice onset measures using methods of assessment which could easily and efficiently be applied in clinical contexts, as well as validation of these individual measures. In addition, further research into standardised measurement criteria and voice assessment protocols which incorporate clinically viable measures of vowel initial voice onset would prove valuable. Given that vowel-initial voice onset measures provide useful information for all voice disorder populations, diverse populations and disorder types would need to be considered. Performing effect size calculations which are clearly documented in the resulting manuscript, and seeking large study populations wherever possible should be prioritised.

Further research should also perform independent auditory perceptual ratings of samples for cross-comparison; ideally using publicly available voice databases wherever possible. It is also of utmost importance that future voice onset research presents a physiological definition of what precisely each study will measure, rather than measuring voice onset solely according to perceptual judgements of voice onset type. In the same vein, these studies must also ensure that the measure they select is able to assess these physiological features, rather than base a measurement upon inference. The development of such research would lead to far greater confidence in the collective findings across the vowel-initial voice onset literature, and an ability to develop informed recommendations pertaining to the application of these measures in a clinical capacity.

Voice onset is a highly variable event involving multiple physiological processes and as such, is a difficult phenomenon to measure. The findings of this review do not permit us to provide informed recommendations regarding the most reliable, sensitive and specific means of measuring vowel-initial voice onset, due to the heterogeneity and overall low research quality of the examined studies. There is a clear need for high-quality data and well-designed research which examines voicing control across the lifespan and across disorders. Ideally, this should compare a range of measures, particularly those which would be easily practicable in clinical scenarios, and provide a robust evaluation of their reliability, sensitivity and specificity in patient-based contexts.

Supporting information

S1 checklist. prisma 2020 checklist..

https://doi.org/10.1371/journal.pone.0301786.s001

S1 File. Systematic review protocol.

https://doi.org/10.1371/journal.pone.0301786.s002

S2 File. Database search strategy.

https://doi.org/10.1371/journal.pone.0301786.s003

S3 File. Data extraction summary table.

https://doi.org/10.1371/journal.pone.0301786.s004

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• 35. Kunduk M. Use of high-speed imaging to describe the voice initiation period in younger and older females: The University of Wisconsin—Madison; 2004. (Paper access: https://www.proquest.com/docview/305110380/fulltextPDF/D87B7273B21F481CPQ/20?accountid=14757&sourcetype=Dissertations%20&%20Theses ).
• 41. Schünemann H, Brożek J, Guyatt G, Oxman A. The GRADE handbook: Cochrane Collaboration London, UK; 2013. Available from: https://gdt.gradepro.org/app/handbook/handbook.html

Book Review: Memoirist Lilly Dancyger’s penetrating essays explore the power of female friendships

In 2021 Lilly Dancyger’s first book, “Negative Space,” was praised for its unflinching portrait of her father’s heroin addiction

Who means more to you — your friends or your lovers? In a vivid, thoughtful and nuanced collection of essays, Lilly Dancyger explores the powerful role that female friendships played in her chaotic upbringing marked by her parents’ heroin use and her father’s untimely death when she was only 12.

“First Love: Essays on Friendship” begins with a beautiful paean to her cousin Sabina, who was raped and murdered at age 20 on her way home from a club. As little kids, their older relatives used to call them Snow White and Rose Red after the Grimm’s fairy tale, “two sisters who are not rivals or foils, but simply love each other.”

That simple, uncomplicated love would become the template for a series of subsequent relationships with girls and women that helped her survive her self-destructive adolescence and provided unconditional support as she scrambled to create a new identity as a “hypercompetent” writer, teacher and editor. “It’s true that I’ve never been satisfied with friendships that stay on the surface. That my friends are my family, my truest beloveds, each relationship a world of its own,” she writes in the title essay “First Love.”

The collection stands out not just for its elegant, unadorned writing but also for the way she effortlessly pivots between personal history and spot-on cultural criticism that both comments on and critiques the way that girls and women have been portrayed — and have portrayed themselves — in the media, including on online platforms like Tumblr and Instagram.

For instance, she examines the 1994 Peter Jackson film, “Heavenly Creatures,” based on the true story of two teenage girls who bludgeoned to death one of their mothers. And in the essay “Sad Girls,” about the suicide of a close friend, she analyzes the allure of self-destructive figures like Sylvia Plath and Janis Joplin to a certain type of teen, including herself, who wallows in sadness and wants to make sure “the world knew we were in pain.”

In the last essay, “On Murder Memoirs,” Dancyger considers the runaway popularity of true crime stories as she tries to explain her decision not to attend the trial of the man charged with killing her cousin — even though she was trained as a journalist and wrote a well-regarded book about her late father that relied on investigative reporting. “When I finally sat down to write about Sabina, the story that came out was not about murder at all,” she says. “It was a love story.”

Readers can be thankful that it did.

AP book reviews: https://apnews.com/hub/book-reviews

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Essay: Quantum Sensing with Atomic, Molecular, and Optical Platforms for Fundamental Physics

Jun ye and peter zoller, phys. rev. lett. 132 , 190001 – published 7 may 2024.

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• Introduction.—
• Emerging quantum technologies based on…
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Atomic, molecular, and optical (AMO) physics has been at the forefront of the development of quantum science while laying the foundation for modern technology. With the growing capabilities of quantum control of many atoms for engineered many-body states and quantum entanglement, a key question emerges: what critical impact will the second quantum revolution with ubiquitous applications of entanglement bring to bear on fundamental physics? In this Essay, we argue that a compelling long-term vision for fundamental physics and novel applications is to harness the rapid development of quantum information science to define and advance the frontiers of measurement physics, with strong potential for fundamental discoveries. As quantum technologies, such as fault-tolerant quantum computing and entangled quantum sensor networks, become much more advanced than today’s realization, we wonder what doors of basic science can these tools unlock. We anticipate that some of the most intriguing and challenging problems, such as quantum aspects of gravity, fundamental symmetries, or new physics beyond the minimal standard model, will be tackled at the emerging quantum measurement frontier.

Part of a series of Essays which concisely present author visions for the future of their field .

• Received 28 March 2024

DOI: https://doi.org/10.1103/PhysRevLett.132.190001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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• JILA, National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
• Institute for Theoretical Physics, University of Innsbruck, 6020 Innsbruck, Austria and Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, 6020 Innsbruck, Austria

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Vol. 132, Iss. 19 — 10 May 2024

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Quantum system design and engineering to open new frontiers for quantum sensing. (a) A quantum network that links individual clocks in space with enhanced performance and security based on their entangled quantum states. The optimal use of global resources and quantum-enabled precision and accuracy also represent a unique long-baseline observatory for fundamental physics [ 6 ]. (b) A Wannier-Stark optical lattice where clock (spin) and atom interferometer (motion) are integrated into a single quantum platform [ 7 ]. Cavity-QED-based entanglement generation will further enhance the probing of clock frequency, coherence, and gravity [ 8 ]. (c) A new monolithic ion trap configuration allows a two-dimensional arrangement of laser-cooled ions for quantum simulations of spin models and increased sensing capabilities [ 9 ]. (d) A tweezer array of neutral atoms that enable any-to-any connectivity among hundreds of atomic qubits with universal local single-qubit rotations and high-fidelity two-qubit Rydberg gates. Fast midcircuit readout and feedforward can be implemented together with parallel transport in reconfigurable array architecture [ 10, 11 ]. (e) The generation of GHZ entangled states for enhanced interferometric sensitivity in clock operation, reaching the Heisenberg limit where the phase sensitivity scales with the inverse of particle number N . This is the best possible outcome defined by quantum physics [ 11, 12 ].

Peter Zoller

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Book Review: Memoirist Lilly Dancyger’s penetrating essays explore the power of female friendships

This cover image released by Dial Press shows “First Love” by Lilly Dancyger. (Dial Press via AP)

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Who means more to you — your friends or your lovers? In a vivid, thoughtful and nuanced collection of essays, Lilly Dancyger explores the powerful role that female friendships played in her chaotic upbringing marked by her parents’ heroin use and her father’s untimely death when she was only 12.

“First Love: Essays on Friendship” begins with a beautiful paean to her cousin Sabina, who was raped and murdered at age 20 on her way home from a club. As little kids, their older relatives used to call them Snow White and Rose Red after the Grimm’s fairy tale, “two sisters who are not rivals or foils, but simply love each other.”

That simple, uncomplicated love would become the template for a series of subsequent relationships with girls and women that helped her survive her self-destructive adolescence and provided unconditional support as she scrambled to create a new identity as a “hypercompetent” writer, teacher and editor. “It’s true that I’ve never been satisfied with friendships that stay on the surface. That my friends are my family, my truest beloveds, each relationship a world of its own,” she writes in the title essay “First Love.”

The collection stands out not just for its elegant, unadorned writing but also for the way she effortlessly pivots between personal history and spot-on cultural criticism that both comments on and critiques the way that girls and women have been portrayed — and have portrayed themselves — in the media, including on online platforms like Tumblr and Instagram.

For instance, she examines the 1994 Peter Jackson film, “Heavenly Creatures,” based on the true story of two teenage girls who bludgeoned to death one of their mothers. And in the essay “Sad Girls,” about the suicide of a close friend, she analyzes the allure of self-destructive figures like Sylvia Plath and Janis Joplin to a certain type of teen, including herself, who wallows in sadness and wants to make sure “the world knew we were in pain.”

In the last essay, “On Murder Memoirs,” Dancyger considers the runaway popularity of true crime stories as she tries to explain her decision not to attend the trial of the man charged with killing her cousin — even though she was trained as a journalist and wrote a well-regarded book about her late father that relied on investigative reporting. “When I finally sat down to write about Sabina, the story that came out was not about murder at all,” she says. “It was a love story.”

Readers can be thankful that it did.

AP book reviews: https://apnews.com/hub/book-reviews

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A Modern Mom Finds an Ancient Outlet for Feminist Rage

In Alexis Landau’s ambitious new novel, “The Mother of All Things,” the frustrations of modern parenting echo through the ages.

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Eliza Minot is the author of the novels “The Tiny One,” “The Brambles” and, most recently, “In the Orchard.”

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THE MOTHER OF ALL THINGS, by Alexis Landau

What is the source of maternal rage? The answer is as infinite as it is ancient. In 1965, the poet and essayist Adrienne Rich, with small children underfoot, captured a possible explanation for this abyss in her journal when she described it as “a sense of insufficiency to the moment and to eternity.”

But where — for moms, for women — does this nagging feeling of insufficiency come from? From the misogyny that we grow up with? From the helpless outrage we bear as our messy, gorgeous, individual maternal experiences are flattened by society into a weirdly infantilized stereotype that’s placed, like a paper doll, into a two-dimensional dollhouse called “Motherhood”? Or does it come from the profound feeling of helplessness that accompanies the ability to give life to a human being, but be unable to ensure that life’s safety?

Ava Zaretsky, the diligent heroine of Alexis Landau’s ambitious and engaging new novel, “The Mother of All Things” (her third after “Those Who Are Saved” and “The Emperor of the Senses”), simmers with a steady rage that never fully erupts toward her kids (Sam, 10, and Margot, 13, who’s at the edge of “adolescence’s dark tunnel”) or her husband, Kasper, a preoccupied Los Angeles film producer. Rather, Ava’s rage burns beneath the surface, “so white and hot it blurred the contours of her body.” She is angry that, in a marriage of supposed equals circa 2019, Kasper can relocate to Sofia, Bulgaria, for a six-month film shoot without a second thought, while her own work as an adjunct art history professor is smudged out by the needs of her family. Her fury is also embedded, we later learn, in the powerlessness that comes with profound loss.

When the family joins Kasper in Sofia for the summer, the kids enroll in a day camp, allowing Ava to wander this mysterious city. Her curiosity and creativity bubble to the surface. She begins writing about an ancient Greek woman whose life parallels and dovetails with her own, and whose narrative is interspersed throughout the pages of the novel. By coincidence, Ava also reconnects in Sofia with an intimidating former professor named Lydia Nikitas and becomes involved in a group of women who participate in re-enactments of ancient rites and rituals, most notably the Eleusinian Mysteries.

Despite some moments that feel forced and overly earnest, particularly in the ancient narrative and the Nikitas story line, Landau’s writing is accessible, specific, lush and transporting. Her research is rigorous and full of elegant effort. The great success of this novel is the author’s sustained exploration of a woman in early midlife who, seething quietly on the inside but operating gracefully on the outside, bravely re-evaluates how her life has unfolded in order to progress as a mother to herself. Renderings of Ava’s childhood — a heartbreaking recollection of a favorite red belt, memories of a father’s girlfriend entering her life and then leaving it — are especially astute and rich.

At times, the novel’s disparate parts compete with rather than complement one another; some characters seem predictable, and certain ideas redundant. When things are meant to get weird, as in the rituals, it can feel more Scooby-Doo than genuinely haunting. For this reason, more than once, I felt like shaking the book like a snow globe, as if its fascinating contents, suspended, might set free more of its wildness.

Landau’s prose can also lift off the page, as it does in a prolonged memory of Ava’s first childbirth and its aftermath. Here, Landau’s writing is intimate, tender and full of terror. The sentences breathe with the softness of shared human experience across time — absolutely sufficient to the moment, and to eternity, too.

THE MOTHER OF ALL THINGS | By Alexis Landau | Pantheon | 336 pp. | $29

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Like Love by Maggie Nelson review – music, passion and friendship

Vibrant essays from the author of The Argonauts touch on art, inspiration, and many of the central dilemmas of our times

“A s a child I had so much energy I’d lie awake and feel my organs smolder,” Maggie Nelson wrote in 2005’s Jane: A Murder . She was a dancer before she was a writer and you can feel the commitment to the fire of bodily motion in her masterpieces: the shimmeringly brutal excavation of girlhood and violence in Jane , the story of her aunt’s killing at the hands of a rapist; the clear-headed yet ecstatic celebration of the transformations of pregnancy and top surgery, and the new kind of family she and her trans partner brought into being in The Argonauts (2015). Her dedication to the material finds the forms it needs; I don’t think she sets out to bend genres. Instead, her high-stakes eviscerations of body settle into radically new forms.

Is this the energy of the rebel or the valedictorian? For decades, Nelson has parted her hair, fastened her top button, won the right grades and grants while throwing herself voluptuously into the counterculture, dreaming of being an “ electric ribbon of horniness and divine grace ” like one of her inspirations, Prince . It’s an American energy – expansive, new, full of power, pleasure, change and motion; a frontier energy, even when she’s writing about New York. We can hear Whitman behind her, and Emerson. “Power ceases in the instant of repose,” Emerson pronounces in Self-Reliance ; “it resides in the moment of transition from a past to a new state, in the shooting of a gulf, in the darting to an aim.”

A decade after The Argonauts became the bible of English graduates everywhere, the essays in Like Love arrive to help us understand Nelson’s place in a culture where, to her half-delight, she has become such a powerful voice. Spanning two decades, they range from appreciations of influences including Prince and Judith Butler , to wild, freefalling conversations with figures such as Björk, Wayne Koestenbaum and Jacqueline Rose. There is a passionate, wondering account of her formative half-erotic friendship with the singer Lhasa de Sela . The writing isn’t consistent, any more than her books are. But I like to take my thinkers and writers whole, as she does. The essays offer a kind of composite self-portrait, and illustrate how she thinks, sometimes painstakingly, sometimes with casual jubilance, about some of the central dilemmas of our time.

In the face of the climate crisis, how to avoid “giving in to the narcissistic spectacle of the slo-mo Titanic going down”? In the face of the crisis in feminism, how and whether to move beyond sexual difference? The written exchanges show her interlocutors thinking it through, too. “ You dare to step into the future like no one else atm ,” Björk says. It’s true. This is where all that restless energy is leading. This is why she’s an Emersonian, shying away from nihilism. “There are new lands, new men, new thoughts,” Emerson wrote in Nature , discarding the “dry bones” of his ancestors; “Let us demand our own works and laws and worship.”

In her powerful piece on the artist Carolee Schneemann , Nelson posits her as a female incarnation of Emerson’s self-reliant man. But it’s Nelson herself who proffers new laws and worship – whose project amounts to a practical philosophy of contemporary American culture. In The Argonauts she offers the gift of a future we can somehow share; one that acknowledges the miseries of the present, that has space for dreams, but is obstinately material and in our world. Here, in dialogue with Jacqueline Rose, she proposes that “ Everybody deserves the kind of non-stultifying internal breathing space of fluidity or instability that is attributed to queers, or to women, or whatever.”

Like Love’s title comes from theatre critic Hilton Als ’s vision of a group on the subway not as white women or black men but as mouths that need filling “with something wet or dry, like love, or unfamiliar and savory, like love”. Nelson, too, is drawn to mouths – to orifices in general – as organs of pleasure and pain, and as portals enabling a radical openness.

Because Nelson likes writing about her friends, there’s a kind of homogeneity to much of the book that cumulatively left me feeling a little claustrophobic, longing especially for the roominess of time travel. With the exception of 2009’s Bluets , Nelson’s writing is so located in the postwar world that the past can feel entirely absent. This is her affinity with Emerson and Whitman again – her song to the future – but I wonder if I’m alone in wishing that, alongside those two often acknowledged ancestors, her future could have artists, activists and libertines from earlier centuries informing it, too.

Which is not to say that she’s wrong to write about the people in her circle. The brutality of the present moment may require us precisely to batten down the hatches and commit to extreme solidarity. At a time when institutional life is collapsing, when the pandemic privileged family over friends, when work expands in ways that leave many too exhausted to socialise, Nelson demonstrates what it means to dedicate yourself to a cohort with seriousness and strenuousness. “You, to me, quickly became an inspiration,” she tells the poet Brian Blanchfield , “a brother, a support in times of seriously dark waters, an editor, a lender of excellent and pivotal books, a cheerleader, a colleague, a couch sleeper (and couch mover), a fellow swimmer … a corrupting gambler, (queer) family.” Like Love may be one of the most movingly specific, the most lovingly unruly celebrations of the ethics of friendship we have.

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