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What are Systematic Reviews? (3 minutes, 24 second YouTube Video)

Systematic Literature Reviews: Steps & Resources

These steps for conducting a systematic literature review are listed below . 

Also see subpages for more information about:

• The different types of literature reviews, including systematic reviews and other evidence synthesis methods
• Tools & Tutorials

Literature Review & Systematic Review Steps

• Develop a Focused Question
• Scope the Literature  (Initial Search)
• Refine & Expand the Search
• Limit the Results
• Download Citations
• Abstract & Analyze
• Create Flow Diagram
• Synthesize & Report Results

1. Develop a Focused   Question 

Consider the PICO Format: Population/Problem, Intervention, Comparison, Outcome

Focus on defining the Population or Problem and Intervention (don't narrow by Comparison or Outcome just yet!)

"What are the effects of the Pilates method for patients with low back pain?"

Tools & Additional Resources:

• PICO Question Help
• Stillwell, Susan B., DNP, RN, CNE; Fineout-Overholt, Ellen, PhD, RN, FNAP, FAAN; Melnyk, Bernadette Mazurek, PhD, RN, CPNP/PMHNP, FNAP, FAAN; Williamson, Kathleen M., PhD, RN Evidence-Based Practice, Step by Step: Asking the Clinical Question, AJN The American Journal of Nursing : March 2010 - Volume 110 - Issue 3 - p 58-61 doi: 10.1097/01.NAJ.0000368959.11129.79

2. Scope the Literature

A "scoping search" investigates the breadth and/or depth of the initial question or may identify a gap in the literature. 

Eligible studies may be located by searching in:

• Background sources (books, point-of-care tools)
• Article databases
• Trial registries
• Grey literature
• Cited references
• Reference lists

When searching, if possible, translate terms to controlled vocabulary of the database. Use text word searching when necessary.

Use Boolean operators to connect search terms:

• Combine separate concepts with AND  (resulting in a narrower search)
• Connecting synonyms with OR  (resulting in an expanded search)

Search:  pilates AND ("low back pain"  OR  backache )

Video Tutorials - Translating PICO Questions into Search Queries

• Translate Your PICO Into a Search in PubMed (YouTube, Carrie Price, 5:11) 
• Translate Your PICO Into a Search in CINAHL (YouTube, Carrie Price, 4:56)

3. Refine & Expand Your Search

Expand your search strategy with synonymous search terms harvested from:

• database thesauri
• reference lists
• relevant studies

Example: 

(pilates OR exercise movement techniques) AND ("low back pain" OR backache* OR sciatica OR lumbago OR spondylosis)

As you develop a final, reproducible strategy for each database, save your strategies in a:

• a personal database account (e.g., MyNCBI for PubMed)
• Log in with your NYU credentials
• Open and "Make a Copy" to create your own tracker for your literature search strategies

4. Limit Your Results

Use database filters to limit your results based on your defined inclusion/exclusion criteria.  In addition to relying on the databases' categorical filters, you may also need to manually screen results.  

• Limit to Article type, e.g.,:  "randomized controlled trial" OR multicenter study
• Limit by publication years, age groups, language, etc.

NOTE: Many databases allow you to filter to "Full Text Only".  This filter is  not recommended . It excludes articles if their full text is not available in that particular database (CINAHL, PubMed, etc), but if the article is relevant, it is important that you are able to read its title and abstract, regardless of 'full text' status. The full text is likely to be accessible through another source (a different database, or Interlibrary Loan).  

• Filters in PubMed
• CINAHL Advanced Searching Tutorial

5. Download Citations

Selected citations and/or entire sets of search results can be downloaded from the database into a citation management tool. If you are conducting a systematic review that will require reporting according to PRISMA standards, a citation manager can help you keep track of the number of articles that came from each database, as well as the number of duplicate records.

In Zotero, you can create a Collection for the combined results set, and sub-collections for the results from each database you search.  You can then use Zotero's 'Duplicate Items" function to find and merge duplicate records.

• Citation Managers - General Guide

6. Abstract and Analyze

• Migrate citations to data collection/extraction tool
• Screen Title/Abstracts for inclusion/exclusion
• Screen and appraise full text for relevance, methods, 
• Resolve disagreements by consensus

Covidence is a web-based tool that enables you to work with a team to screen titles/abstracts and full text for inclusion in your review, as well as extract data from the included studies.

• Covidence Support
• Critical Appraisal Tools
• Data Extraction Tools

7. Create Flow Diagram

The PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) flow diagram is a visual representation of the flow of records through different phases of a systematic review.  It depicts the number of records identified, included and excluded.  It is best used in conjunction with the PRISMA checklist .

Example from: Stotz, S. A., McNealy, K., Begay, R. L., DeSanto, K., Manson, S. M., & Moore, K. R. (2021). Multi-level diabetes prevention and treatment interventions for Native people in the USA and Canada: A scoping review. Current Diabetes Reports, 2 (11), 46. https://doi.org/10.1007/s11892-021-01414-3

• PRISMA Flow Diagram Generator (ShinyApp.io, Haddaway et al. )
• PRISMA Diagram Templates  (Word and PDF)
• Make a copy of the file to fill out the template
• Image can be downloaded as PDF, PNG, JPG, or SVG
• Covidence generates a PRISMA diagram that is automatically updated as records move through the review phases

8. Synthesize & Report Results

There are a number of reporting guideline available to guide the synthesis and reporting of results in systematic literature reviews.

It is common to organize findings in a matrix, also known as a Table of Evidence (ToE).

• Reporting Guidelines for Systematic Reviews
• Download a sample template of a health sciences review matrix  (GoogleSheets)

Steps modified from: 

Cook, D. A., & West, C. P. (2012). Conducting systematic reviews in medical education: a stepwise approach.   Medical Education , 46 (10), 943–952.

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A necessary skill for any doctor

What causes disease, which drug is best, does this patient need surgery, and what is the prognosis? Although experience helps in answering these questions, ultimately they are best answered by evidence based medicine. But how do you assess the evidence? As a medical student, and throughout your career as a doctor, critical appraisal of published literature is an important skill to develop and refine. At medical school you will repeatedly appraise published literature and write literature reviews. These activities are commonly part of a special study module, research project for an intercalated degree, or another type of essay based assignment.

Formulating a question

Literature reviews are most commonly performed to help answer a particular question. While you are at medical school, there will usually be some choice regarding the area you are going to review.

Once you have identified a subject area for review, the next step is to formulate a specific research question. This is arguably the most important step because a clear question needs to be defined from the outset, which you aim to answer by doing the review. The clearer the question, the more likely it is that the answer will be clear too. It is important to have discussions with your supervisor when formulating a research question as his or her input will be invaluable. The research question must be objective and concise because it is easier to search through the evidence with a clear question. The question also needs to be feasible. What is the point in having a question for which no published evidence exists? Your supervisor’s input will ensure you are not trying to answer an unrealistic question. Finally, is the research question clinically important? There are many research questions that may be answered, but not all of them will be relevant to clinical practice. The research question we will use as an example to work through in this article is, “What is the evidence for using angiotensin converting enzyme (ACE) inhibitors in patients with hypertension?”

Collecting the evidence

After formulating a specific research question for your literature review, the next step is to collect the evidence. Your supervisor will initially point you in the right direction by highlighting some of the more relevant papers published. Before doing the literature search it is important to agree a list of keywords with your supervisor. A source of useful keywords can be obtained by reading Cochrane reviews or other systematic reviews, such as those published in the BMJ . 1 2 A relevant Cochrane review for our research question on ACE inhibitors in hypertension is that by Heran and colleagues. 3 Appropriate keywords to search for the evidence include the words used in your research question (“angiotensin converting enzyme inhibitor,” “hypertension,” “blood pressure”), details of the types of study you are looking for (“randomised controlled trial,” “case control,” “cohort”), and the specific drugs you are interested in (that is, the various ACE inhibitors such as “ramipril,” “perindopril,” and “lisinopril”).

Once keywords have been agreed it is time to search for the evidence using the various electronic medical databases (such as PubMed, Medline, and EMBASE). PubMed is the largest of these databases and contains online information and tutorials on how to do literature searches with worked examples. Searching the databases and obtaining the articles are usually free of charge through the subscription that your university pays. Early consultation with a medical librarian is important as it will help you perform your literature search in an impartial manner, and librarians can train you to do these searches for yourself.

Literature searches can be broad or tailored to be more specific. With our example, a broad search would entail searching all articles that contain the words “blood pressure” or “ACE inhibitor.” This provides a comprehensive list of all the literature, but there are likely to be thousands of articles to review subsequently (fig 1). ⇓ In contrast, various search restrictions can be applied on the electronic databases to filter out papers that may not be relevant to your review. Figure 2 gives an example of a specific search. ⇓ The search terms used in this case were “angiotensin converting enzyme inhibitor” and “hypertension.” The limits applied to this search were all randomised controlled trials carried out in humans, published in the English language over the last 10 years, with the search terms appearing in the title of the study only. Thus the more specific the search strategy, the more manageable the number of articles to review (fig 3), and this will save you time. ⇓ However, this method risks your not identifying all the evidence in the particular field. Striking a balance between a broad and a specific search strategy is therefore important. This will come with experience and consultation with your supervisor. It is important to note that evidence is continually becoming available on these electronic databases and therefore repeating the same search at a later date can provide new evidence relevant to your review.

Fig 1 Results from a broad literature search using the term “angiotensin converting enzyme inhibitor”

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Fig 2 Example of a specific literature search. The search terms used were “angiotensin converting enzyme inhibitor” and “hypertension.” The limits applied to this search were all randomised controlled trials carried out in humans, published in English over the past 10 years, with the search terms appearing in the title of the study only

Fig 3 Results from a specific literature search (using the search terms and limits from figure 2)

Reading the abstracts (study summary) of the articles identified in your search may help you decide whether the study is applicable for your review—for example, the work may have been carried out using an animal model rather than in humans. After excluding any inappropriate articles, you need to obtain the full articles of studies you have identified. Additional relevant articles that may not have come up in your original search can also be found by searching the reference lists of the articles you have already obtained. Once again, you may find that some articles are still not applicable for your review, and these can also be excluded at this stage. It is important to explain in your final review what criteria you used to exclude articles as well as those criteria used for inclusion.

The National Institute for Health and Clinical Excellence (NICE) publishes evidence based guidelines for the United Kingdom and therefore provides an additional resource for identifying the relevant literature in a particular field. 4 NICE critically appraises the published literature with recommendations for best clinical practice proposed and graded based on the quality of evidence available. Similarly, there are internationally published evidence based guidelines, such as those produced by the European Society of Cardiology and the American College of Chest Physicians, which can be useful when collecting the literature in a particular field. 5 6

Appraising the evidence

Once you have collected the evidence, you need to critically appraise the published material. Box 1 gives definitions of terms you will encounter when reading the literature. A brief guide of how to critically appraise a study is presented; however, it is advisable to consult the references cited for further details.

Box 1: Definitions of common terms in the literature 7

Prospective—collecting data in real time after the study is designed

Retrospective—analysis of data that have already been collected to determine associations between exposure and outcome

Hypothesis—proposed association between exposure and outcome. If presented in the negative it is called the null hypothesis

Variable—a quantity or quality that changes during the study and can be measured

Single blind—subjects are unaware of their treatment, but clinicians are aware

Double blind—both subjects and clinicians are unaware of treatment given

Placebo—a simulated medical intervention, with subjects not receiving the specific intervention or treatment being studied

Outcome measure/endpoint—clinical variable or variables measured in a study subsequently used to make conclusions about the original interventions or treatments administered

Bias—difference between reported results and true results. Many types exist (such as selection, allocation, and reporting biases)

Probability (P) value—number between 0 and 1 providing the likelihood the reported results occurred by chance. A P value of 0.05 means there is a 5% likelihood that the reported result occurred by chance

Confidence intervals—provides a range between two numbers within which one can be certain the results lie. A confidence interval of 95% means one can be 95% certain the actual results lie within the reported range

The study authors should clearly define their research question and ideally the hypothesis to be tested. If the hypothesis is presented in the negative, it is called the null hypothesis. An example of a null hypothesis is smoking does not cause lung cancer. The study is then performed to assess the significance of the exposure (smoking) on outcome (lung cancer).

A major part of the critical appraisal process is to focus on study methodology, with your key task being an assessment of the extent to which a study was susceptible to bias (the discrepancy between the reported results and the true results). It should be clear from the methods what type of study was performed (box 2).

Box 2: Different study types 7

Systematic review/meta-analysis—comprehensive review of published literature using predefined methodology. Meta-analyses combine results from various studies to give numerical data for the overall association between variables

Randomised controlled trial—random allocation of patients to one of two or more groups. Used to test a new drug or procedure

Cohort study—two or more groups followed up over a long period, with one group exposed to a certain agent (drug or environmental agent) and the other not exposed, with various outcomes compared. An example would be following up a group of smokers and a group of non-smokers with the outcome measure being the development of lung cancer

Case-control study—cases (those with a particular outcome) are matched as closely as possible (for age, sex, ethnicity) with controls (those without the particular outcome). Retrospective data analysis is performed to determine any factors associated with developing the particular outcomes

Cross sectional study—looks at a specific group of patients at a single point in time. Effectively a survey. An example is asking a group of people how many of them drink alcohol

Case report—detailed reports concerning single patients. Useful in highlighting adverse drug reactions

There are many different types of bias, which depend on the particular type of study performed, and it is important to look for these biases. Several published checklists are available that provide excellent resources to help you work through the various studies and identify sources of bias. The CONSORT statement (which stands for CONsolidated Standards Of Reporting Trials) provides a minimum set of recommendations for reporting randomised controlled trials and comprises a rigorous 25 item checklist, with variations available for other study types. 8 9 As would be expected, most (17 of 25) of the items focus on questions relating to the methods and results of the randomised trial. The remaining items relate to the title, abstract, introduction, and discussion of the study, in addition to questions on trial registration, protocol, and funding.

Jadad scoring provides a simple and validated system to assess the methodological quality of a randomised clinical trial using three questions. 10 The score ranges from zero to five, with one point given for a “yes” in each of the following questions. (1) Was the study described as randomised? (2) Was the study described as double blind? (3) Were there details of subject withdrawals, exclusions, and dropouts? A further point is given if (1) the method of randomisation was appropriate, and (2) the method of blinding was appropriate.

In addition, the Critical Appraisal Skills Programme provides excellent tools for assessing the evidence in all study types (box 2). 11 The Oxford Centre for Evidence-Based Medicine levels of evidence is yet another useful resource for assessing the methodological quality of all studies. 12

Ensure all patients have been accounted for and any exclusions, for whatever reason, are reported. Knowing the baseline demographic (age, sex, ethnicity) and clinical characteristics of the population is important. Results are usually reported as probability values or confidence intervals (box 1).

This should explain the major study findings, put the results in the context of the published literature, and attempt to account for any variations from previous work. Study limitations and sources of bias should be discussed. Authors’ conclusions should be supported by the study results and not unnecessarily extrapolated. For example, a treatment shown to be effective in animals does not necessarily mean it will work in humans.

The format for writing up the literature review usually consists of an abstract (short structured summary of the review), the introduction or background, methods, results, and discussion with conclusions. There are a number of good examples of how to structure a literature review and these can be used as an outline when writing your review. 13 14

The introduction should identify the specific research question you intend to address and briefly put this into the context of the published literature. As you have now probably realised, the methods used for the review must be clear to the reader and provide the necessary detail for someone to be able to reproduce the search. The search strategy needs to include a list of keywords used, which databases were searched, and the specific search limits or filters applied. Any grading of methodological quality, such as the CONSORT statement or Jadad scoring, must be explained in addition to any study inclusion or exclusion criteria. 6 7 8 The methods also need to include a section on the data collected from each of the studies, the specific outcomes of interest, and any statistical analysis used. The latter point is usually relevant only when performing meta-analyses.

The results section must clearly show the process of filtering down from the articles obtained from the original search to the final studies included in the review—that is, accounting for all excluded studies. A flowchart is usually best to illustrate this. Next should follow a brief description of what was done in the main studies, the number of participants, the relevant results, and any potential sources of bias. It is useful to group similar studies together as it allows comparisons to be made by the reader and saves repetition in your write-up. Boxes and figures should be used appropriately to illustrate important findings from the various studies.

Finally, in the discussion you need to consider the study findings in light of the methodological quality—that is, the extent of potential bias in each study that may have affected the study results. Using the evidence, you need to make conclusions in your review, and highlight any important gaps in the evidence base, which need to be dealt with in future studies. Working through drafts of the literature review with your supervisor will help refine your critical appraisal skills and the ability to present information concisely in a structured review article. Remember, if the work is good it may get published.

Originally published as: Student BMJ 2012;20:e404

Competing interests: None declared.

Provenance and peer review: Not commissioned; externally peer reviewed.

• ↵ The Cochrane Library. www3.interscience.wiley.com/cgibin/mrwhome/106568753/HOME?CRETRY=1&SRETRY=0 .
• ↵ British Medical Journal . www.bmj.com/ .
• ↵ Heran BS, Wong MMY, Heran IK, Wright JM. Blood pressure lowering efficacy of angiotensin converting enzyme (ACE) inhibitors for primary hypertension. Cochrane Database Syst Rev 2008 ; 4 : CD003823 , doi: 10.1002/14651858.CD003823.pub2. OpenUrl PubMed
• ↵ National Institute for Health and Clinical Excellence. www.nice.org.uk .
• ↵ European Society of Cardiology. www.escardio.org/guidelines .
• ↵ Geerts WH, Bergqvist D, Pineo GF, Heit JA, Samama CM, Lassen MR, et al. Prevention of venous thromboembolism: American College of Chest Physicians evidence-based clinical practice guidelines (8th ed). Chest 2008 ; 133 : 381 -453S. OpenUrl CrossRef
• ↵ Wikipedia. http://en.wikipedia.org/wiki .
• ↵ Moher D, Schulz KF, Altman DG, Egger M, Davidoff F, Elbourne D, et al. The CONSORT statement: revised recommendations for improving the quality of reports of parallel-group randomised trials. Lancet 2001 ; 357 : 1191 -4. OpenUrl CrossRef PubMed Web of Science
• ↵ The CONSORT statement. www.consort-statement.org/ .
• ↵ Jadad AR, Moore RA, Carroll D, Jenkinson C, Reynolds DJ, Gavaghan DJ, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials 1996 ; 17 : 1 -12. OpenUrl CrossRef PubMed Web of Science
• ↵ Critical Appraisal Skills Programme (CASP). www.sph.nhs.uk/what-we-do/public-health-workforce/resources/critical-appraisals-skills-programme .
• ↵ Oxford Centre for Evidence-based Medicine—Levels of Evidence. www.cebm.net .
• ↵ Van den Bruel A, Thompson MJ, Haj-Hassan T, Stevens R, Moll H, Lakhanpaul M, et al . Diagnostic value of laboratory tests in identifying serious infections in febrile children: systematic review. BMJ 2011 ; 342 : d3082 . OpenUrl Abstract / FREE Full Text
• ↵ Awopetu AI, Moxey P, Hinchliffe RJ, Jones KG, Thompson MM, Holt PJ. Systematic review and meta-analysis of the relationship between hospital volume and outcome for lower limb arterial surgery. Br J Surg 2010 ; 97 : 797 -803. OpenUrl CrossRef PubMed

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• Meeting the review family: exploring review types and associated information retrieval requirements | Health Information and Libraries Journal, 2019
• A typology of reviews: an analysis of 14 review types and associated methodologies | Health Information and Libraries Journal, 2009
• Conceptual recommendations for selecting the most appropriate knowledge synthesis method to answer research questions related to complex evidence | Journal of Clinical Epidemiology, 2016
• Methods for knowledge synthesis: an overview | Heart & Lung: The Journal of Critical Care, 2014
• Not sure what type of review to conduct? Brief descriptions of each type plus tools to help you decide

• Ten simple rules for writing a literature review | PLoS Computational Biology, 2013
• The Purpose, Process, and Methods of Writing a Literature Review | AORN Journal. 2016
• Why, When, Who, What, How, and Where for Trainees Writing Literature Review Articles. | Annals of Biomed Engineering, 2019
• So You Want to Write a Narrative Review Article? | Journal of Cardiothoracic and Anesthesia, 2021
• An Introduction to Writing Narrative and Systematic Reviews - Tasks, Tips and Traps for Aspiring Authors | Heart, Lung, and Circulation, 2018

• The Literature Review: A Foundation for High-Quality Medical Education Research | Journal of Graduate Medical Education, 2016
• Writing an effective literature review : Part I: Mapping the gap | Perspectives on Medical Education, 2018
• Writing an effective literature review : Part II: Citation technique | Perspectives on Medical Education, 2018
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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• 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

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

Scribbr slides are free to use, customize, and distribute for educational purposes.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

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Research bias

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A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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• 04 December 2020
• Correction 09 December 2020

How to write a superb literature review

Andy Tay is a freelance writer based in Singapore.

You can also search for this author in PubMed   Google Scholar

Literature reviews are important resources for scientists. They provide historical context for a field while offering opinions on its future trajectory. Creating them can provide inspiration for one’s own research, as well as some practice in writing. But few scientists are trained in how to write a review — or in what constitutes an excellent one. Even picking the appropriate software to use can be an involved decision (see ‘Tools and techniques’). So Nature asked editors and working scientists with well-cited reviews for their tips.

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doi: https://doi.org/10.1038/d41586-020-03422-x

Interviews have been edited for length and clarity.

Updates & Corrections

Correction 09 December 2020 : An earlier version of the tables in this article included some incorrect details about the programs Zotero, Endnote and Manubot. These have now been corrected.

Hsing, I.-M., Xu, Y. & Zhao, W. Electroanalysis 19 , 755–768 (2007).

Article   Google Scholar  

Ledesma, H. A. et al. Nature Nanotechnol. 14 , 645–657 (2019).

Article   PubMed   Google Scholar  

Brahlek, M., Koirala, N., Bansal, N. & Oh, S. Solid State Commun. 215–216 , 54–62 (2015).

Choi, Y. & Lee, S. Y. Nature Rev. Chem . https://doi.org/10.1038/s41570-020-00221-w (2020).

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Literature Review: Conducting & Writing

• Sample Literature Reviews
• Steps for Conducting a Lit Review
• Finding "The Literature"
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Literature Review Overview

What is a Literature Review? Why Are They Important?

A literature review is important because it presents the "state of the science" or accumulated knowledge on a specific topic. It summarizes, analyzes, and compares the available research, reporting study strengths and weaknesses, results, gaps in the research, conclusions, and authors’ interpretations.

Tips and techniques for conducting a literature review are described more fully in the subsequent boxes:

• Literature review steps
• Strategies for organizing the information for your review
• Literature reviews sections
• In-depth resources to assist in writing a literature review
• Templates to start your review
• Literature review examples

Literature Review Steps

Graphic used with permission: Torres, E. Librarian, Hawai'i Pacific University

1. Choose a topic and define your research question

• Try to choose a topic of interest. You will be working with this subject for several weeks to months.
• Ideas for topics can be found by scanning medical news sources (e.g MedPage Today), journals / magazines, work experiences, interesting patient cases, or family or personal health issues.
• Do a bit of background reading on topic ideas to familiarize yourself with terminology and issues. Note the words and terms that are used.
• Develop a focused research question using PICO(T) or other framework (FINER, SPICE, etc - there are many options) to help guide you.
• Run a few sample database searches to make sure your research question is not too broad or too narrow.
• If possible, discuss your topic with your professor. 

2. Determine the scope of your review

The scope of your review will be determined by your professor during your program. Check your assignment requirements for parameters for the Literature Review.

• How many studies will you need to include?
• How many years should it cover? (usually 5-7 depending on the professor)
• For the nurses, are you required to limit to nursing literature?

3. Develop a search plan

• Determine which databases to search. This will depend on your topic. If you are not sure, check your program specific library website (Physician Asst / Nursing / Health Services Admin) for recommendations.
• Create an initial search string using the main concepts from your research (PICO, etc) question. Include synonyms and related words connected by Boolean operators
• Contact your librarian for assistance, if needed.

4. Conduct searches and find relevant literature

• Keep notes as you search - tracking keywords and search strings used in each database in order to avoid wasting time duplicating a search that has already been tried
• Read abstracts and write down new terms to search as you find them
• Check MeSH or other subject headings listed in relevant articles for additional search terms
• Scan author provided keywords if available
• Check the references of relevant articles looking for other useful articles (ancestry searching)
• Check articles that have cited your relevant article for more useful articles (descendancy searching). Both PubMed and CINAHL offer Cited By links
• Revise the search to broaden or narrow your topic focus as you peruse the available literature
• Conducting a literature search is a repetitive process. Searches can be revised and re-run multiple times during the process.
• Track the citations for your relevant articles in a software citation manager such as RefWorks, Zotero, or Mendeley

5. Review the literature

• Read the full articles. Do not rely solely on the abstracts. Authors frequently cannot include all results within the confines of an abstract. Exclude articles that do not address your research question.
• While reading, note research findings relevant to your project and summarize. Are the findings conflicting? There are matrices available than can help with organization. See the Organizing Information box below.
• Critique / evaluate the quality of the articles, and record your findings in your matrix or summary table. Tools are available to prompt you what to look for. (See Resources for Appraising a Research Study box on the HSA, Nursing , and PA guides )
• You may need to revise your search and re-run it based on your findings.

6. Organize and synthesize

• Compile the findings and analysis from each resource into a single narrative.
• Using an outline can be helpful. Start broad, addressing the overall findings and then narrow, discussing each resource and how it relates to your question and to the other resources.
• Cite as you write to keep sources organized.
• Write in structured paragraphs using topic sentences and transition words to draw connections, comparisons, and contrasts.
• Don't present one study after another, but rather relate one study's findings to another. Speak to how the studies are connected and how they relate to your work.

Organizing Information

Options to assist in organizing sources and information :

1. Synthesis Matrix

• helps provide overview of the literature
• information from individual sources is entered into a grid to enable writers to discern patterns and themes
• article summary, analysis, or results
• thoughts, reflections, or issues
• each reference gets its own row
• mind maps, concept maps, flowcharts
• at top of page record PICO or research question
• record major concepts / themes from literature
• list concepts that branch out from major concepts underneath - keep going downward hierarchically, until most specific ideas are recorded
• enclose concepts in circles and connect the concept with lines - add brief explanation as needed

3. Summary Table

• information is recorded in a grid to help with recall and sorting information when writing
• allows comparing and contrasting individual studies easily
• purpose of study
• methodology (study population, data collection tool)

Efron, S. E., & Ravid, R. (2019). Writing the literature review : A practical guide . Guilford Press.

Literature Review Sections

• Lit reviews can be part of a larger paper / research study or they can be the focus of the paper
• Lit reviews focus on research studies to provide evidence
• New topics may not have much that has been published

* The sections included may depend on the purpose of the literature review (standalone paper or section within a research paper)

Standalone Literature Review (aka Narrative Review):

• presents your topic or PICO question
• includes the why of the literature review and your goals for the review.
• provides background for your the topic and previews the key points
• Narrative Reviews: tmay not have an explanation of methods.
• include where the search was conducted (which databases) what subject terms or keywords were used, and any limits or filters that were applied and why - this will help others re-create the search
• describe how studies were analyzed for inclusion or exclusion
• review the purpose and answer the research question
• thematically - using recurring themes in the literature
• chronologically - present the development of the topic over time
• methodological - compare and contrast findings based on various methodologies used to research the topic (e.g. qualitative vs quantitative, etc.)
• theoretical - organized content based on various theories
• provide an overview of the main points of each source then synthesize the findings into a coherent summary of the whole
• present common themes among the studies
• compare and contrast the various study results
• interpret the results and address the implications of the findings
• do the results support the original hypothesis or conflict with it
• provide your own analysis and interpretation (eg. discuss the significance of findings; evaluate the strengths and weaknesses of the studies, noting any problems)
• discuss common and unusual patterns and offer explanations
•  stay away from opinions, personal biases and unsupported recommendations
• summarize the key findings and relate them back to your PICO/research question
• note gaps in the research and suggest areas for further research
• this section should not contain "new" information that had not been previously discussed in one of the sections above
• provide a list of all the studies and other sources used in proper APA 7

Literature Review as Part of a Research Study Manuscript:

• Compares the study with other research and includes how a study fills a gap in the research.
• Focus on the body of the review which includes the synthesized Findings and Discussion

Literature Reviews vs Systematic Reviews

Systematic Reviews are NOT the same as a Literature Review:

Literature Reviews:

• Literature reviews may or may not follow strict systematic methods to find, select, and analyze articles, but rather they selectively and broadly review the literature on a topic
• Research included in a Literature Review can be "cherry-picked" and therefore, can be very subjective

Systematic Reviews:

• Systemic reviews are designed to provide a comprehensive summary of the evidence for a focused research question
• rigorous and strictly structured, using standardized reporting guidelines (e.g. PRISMA, see link below)
• uses exhaustive, systematic searches of all relevant databases
• best practice dictates search strategies are peer reviewed
• uses predetermined study inclusion and exclusion criteria in order to minimize bias
• aims to capture and synthesize all literature (including unpublished research - grey literature) that meet the predefined criteria on a focused topic resulting in high quality evidence

Literature Review Examples

• Breastfeeding initiation and support: A literature review of what women value and the impact of early discharge (2017). Women and Birth : Journal of the Australian College of Midwives
• Community-based participatory research to promote healthy diet and nutrition and prevent and control obesity among African-Americans: A literature review (2017). Journal of Racial and Ethnic Health Disparities

• Vitamin D deficiency in individuals with a spinal cord injury: A literature review (2017). Spinal Cord

Resources for Writing a Literature Review

These sources have been used in developing this guide.

Resources Used on This Page

Aveyard, H. (2010). Doing a literature review in health and social care : A practical guide . McGraw-Hill Education.

Purdue Online Writing Lab. (n.d.). Writing a literature review . Purdue University. https://owl.purdue.edu/owl/research_and_citation/conducting_research/writing_a_literature_review.html

Torres, E. (2021, October 21). Nursing - graduate studies research guide: Literature review. Hawai'i Pacific University Libraries. Retrieved January 27, 2022, from https://hpu.libguides.com/c.php?g=543891&p=3727230

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What is a literature review?

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The literature review is the qualitative summary of evidence on a topic using informal or subjective methods to collect and interpret studies.The literature review can inform a particular research project or can result in a review article publication.

• Aaron L. Writing a literature review article. Radiol Technol. 2008 Nov-Dec; 80(12): 185-6.
• Gasparyan AY, Ayvazyan L, Blackmore H, Kitas GD. Writing a narrative biomedical review: considerations for authors, peer reviewers, and editors. Rheumatol Int. 2011 Nov; 31(11): 1409-17.
• Matharu GS, Buckley CD. Performing a literature review: a necessary skill for any doctor. Student BMJ. 2012; 20:e404. Requires FREE site registration
• Literature Reviews The Writing Center at University of North Carolina at Chapel Hill has created a succinct handout that explains what a literature review is and offer insights into the form and construction of a literature review in the humanities, social sciences, and sciences.
• Review Articles (Health Sciences) Guide Identifies the difference between a systematic review and a literature review. Connects to tools for research, writing, and publishing.

• Systematic Approaches to a Successful Literature Review by Andrew Booth; Diana Papaioannou; Anthea Sutton Call Number: Norris Medical Library, Upper Level, LB 1047.3 B725s 2012
• Documenting your search This resource provides guidance on how to document and save database search strategies.
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JAY SIWEK, M.D., MARGARET L. GOURLAY, M.D., DAVID C. SLAWSON, M.D., AND ALLEN F. SHAUGHNESSY, PHARM.D.

Am Fam Physician. 2002;65(2):251-258

Traditional clinical review articles, also known as updates, differ from systematic reviews and meta-analyses. Updates selectively review the medical literature while discussing a topic broadly. Nonquantitative systematic reviews comprehensively examine the medical literature, seeking to identify and synthesize all relevant information to formulate the best approach to diagnosis or treatment. Meta-analyses (quantitative systematic reviews) seek to answer a focused clinical question, using rigorous statistical analysis of pooled research studies. This article presents guidelines for writing an evidence-based clinical review article for American Family Physician . First, the topic should be of common interest and relevance to family practice. Include a table of the continuing medical education objectives of the review. State how the literature search was done and include several sources of evidence-based reviews, such as the Cochrane Collaboration, BMJ's Clinical Evidence , or the InfoRetriever Web site. Where possible, use evidence based on clinical outcomes relating to morbidity, mortality, or quality of life, and studies of primary care populations. In articles submitted to American Family Physician , rate the level of evidence for key recommendations according to the following scale: level A (randomized controlled trial [RCT], meta-analysis); level B (other evidence); level C (consensus/expert opinion). Finally, provide a table of key summary points.

American Family Physician is particularly interested in receiving clinical review articles that follow an evidence-based format. Clinical review articles, also known as updates, differ from systematic reviews and meta-analyses in important ways. 1 Updates selectively review the medical literature while discussing a topic broadly. An example of such a topic is, “The diagnosis and treatment of myocardial ischemia.” Systematic reviews comprehensively examine the medical literature, seeking to identify and synthesize all relevant information to formulate the best approach to diagnosis or treatment. Examples are many of the systematic reviews of the Cochrane Collaboration or BMJ's Clinical Evidence compendium. Meta-analyses are a special type of systematic review. They use quantitative methods to analyze the literature and seek to answer a focused clinical question, using rigorous statistical analysis of pooled research studies. An example is, “Do beta blockers reduce mortality following myocardial infarction?”

The best clinical review articles base the discussion on existing systematic reviews and meta-analyses, and incorporate all relevant research findings about the management of a given disorder. Such evidence-based updates provide readers with powerful summaries and sound clinical guidance.

In this article, we present guidelines for writing an evidence-based clinical review article, especially one designed for continuing medical education (CME) and incorporating CME objectives into its format. This article may be read as a companion piece to a previous article and accompanying editorial about reading and evaluating clinical review articles. 1 , 2 Some articles may not be appropriate for an evidence-based format because of the nature of the topic, the slant of the article, a lack of sufficient supporting evidence, or other factors. We encourage authors to review the literature and, wherever possible, rate key points of evidence. This process will help emphasize the summary points of the article and strengthen its teaching value.

Topic Selection

Choose a common clinical problem and avoid topics that are rarities or unusual manifestations of disease or that have curiosity value only. Whenever possible, choose common problems for which there is new information about diagnosis or treatment. Emphasize new information that, if valid, should prompt a change in clinical practice, such as the recent evidence that spironolactone therapy improves survival in patients who have severe congestive heart failure. 3 Similarly, new evidence showing that a standard treatment is no longer helpful, but may be harmful, would also be important to report. For example, patching most traumatic corneal abrasions may actually cause more symptoms and delay healing compared with no patching. 4

Searching the Literature

When searching the literature on your topic, please consult several sources of evidence-based reviews ( Table 1 ) . Look for pertinent guidelines on the diagnosis, treatment, or prevention of the disorder being discussed. Incorporate all high-quality recommendations that are relevant to the topic. When reviewing the first draft, look for all key recommendations about diagnosis and, especially, treatment. Try to ensure that all recommendations are based on the highest level of evidence available. If you are not sure about the source or strength of the recommendation, return to the literature, seeking out the basis for the recommendation.

In particular, try to find the answer in an authoritative compendium of evidence-based reviews, or at least try to find a meta-analysis or well-designed randomized controlled trial (RCT) to support it. If none appears to be available, try to cite an authoritative consensus statement or clinical guideline, such as a National Institutes of Health Consensus Development Conference statement or a clinical guideline published by a major medical organization. If no strong evidence exists to support the conventional approach to managing a given clinical situation, point this out in the text, especially for key recommendations. Keep in mind that much of traditional medical practice has not yet undergone rigorous scientific study, and high-quality evidence may not exist to support conventional knowledge or practice.

Patient-Oriented vs. Disease-Oriented Evidence

With regard to types of evidence, Shaughnessy and Slawson 5 – 7 developed the concept of Patient-Oriented Evidence that Matters (POEM), in distinction to Disease-Oriented Evidence (DOE). POEM deals with outcomes of importance to patients, such as changes in morbidity, mortality, or quality of life. DOE deals with surrogate end points, such as changes in laboratory values or other measures of response. Although the results of DOE sometimes parallel the results of POEM, they do not always correspond ( Table 2 ) . 2 When possible, use POEM-type evidence rather than DOE. When DOE is the only guidance available, indicate that key clinical recommendations lack the support of outcomes evidence. Here is an example of how the latter situation might appear in the text: “Although prostate-specific antigen (PSA) testing identifies prostate cancer at an early stage, it has not yet been proved that PSA screening improves patient survival.” (Note: PSA testing is an example of DOE, a surrogate marker for the true outcomes of importance—improved survival, decreased morbidity, and improved quality of life.)

Evaluating the Literature

Evaluate the strength and validity of the literature that supports the discussion (see the following section, Levels of Evidence). Look for meta-analyses, high-quality, randomized clinical trials with important outcomes (POEM), or well-designed, nonrandomized clinical trials, clinical cohort studies, or case-controlled studies with consistent findings. In some cases, high-quality, historical, uncontrolled studies are appropriate (e.g., the evidence supporting the efficacy of Papanicolaou smear screening). Avoid anecdotal reports or repeating the hearsay of conventional wisdom, which may not stand up to the scrutiny of scientific study (e.g., prescribing prolonged bed rest for low back pain).

Look for studies that describe patient populations that are likely to be seen in primary care rather than subspecialty referral populations. Shaughnessy and Slawson's guide for writers of clinical review articles includes a section on information and validity traps to avoid. 2

Levels of Evidence

Readers need to know the strength of the evidence supporting the key clinical recommendations on diagnosis and treatment. Many different rating systems of varying complexity and clinical relevance are described in the medical literature. Recently, the third U.S. Preventive Services Task Force (USPSTF) emphasized the importance of rating not only the study type (RCT, cohort study, case-control study, etc.), but also the study quality as measured by internal validity and the quality of the entire body of evidence on a topic. 8

While it is important to appreciate these evolving concepts, we find that a simplified grading system is more useful in AFP . We have adopted the following convention, using an ABC rating scale. Criteria for high-quality studies are discussed in several sources. 8 , 9 See the AFP Web site ( www.aafp.org/afp/authors ) for additional information about levels of evidence and see the accompanying editorial in this issue discussing the potential pitfalls and limitations of any rating system.

Level A (randomized controlled trial/meta-analysis): High-quality randomized controlled trial (RCT) that considers all important outcomes. High-quality meta-analysis (quantitative systematic review) using comprehensive search strategies.

Level B (other evidence): A well-designed, nonrandomized clinical trial. A nonquantitative systematic review with appropriate search strategies and well-substantiated conclusions. Includes lower quality RCTs, clinical cohort studies, and case-controlled studies with non-biased selection of study participants and consistent findings. Other evidence, such as high-quality, historical, uncontrolled studies, or well-designed epidemiologic studies with compelling findings, is also included.

Level C (consensus/expert opinion): Consensus viewpoint or expert opinion.

Each rating is applied to a single reference in the article, not to the entire body of evidence that exists on a topic. Each label should include the letter rating (A, B, C), followed by the specific type of study for that reference. For example, following a level B rating, include one of these descriptors: (1) nonrandomized clinical trial; (2) nonquantitative systematic review; (3) lower quality RCT; (4) clinical cohort study; (5) case-controlled study; (6) historical uncontrolled study; (7) epidemiologic study.

Here are some examples of the way evidence ratings should appear in the text:

“To improve morbidity and mortality, most patients in congestive heart failure should be treated with an angiotensin-converting enzyme inhibitor. [Evidence level A, RCT]”

“The USPSTF recommends that clinicians routinely screen asymptomatic pregnant women 25 years and younger for chlamydial infection. [Evidence level B, non-randomized clinical trial]”

“The American Diabetes Association recommends screening for diabetes every three years in all patients at high risk of the disease, including all adults 45 years and older. [Evidence level C, expert opinion]”

When scientifically strong evidence does not exist to support a given clinical recommendation, you can point this out in the following way:

“Physical therapy is traditionally prescribed for the treatment of adhesive capsulitis (frozen shoulder), although there are no randomized outcomes studies of this approach.”

Format of the Review

Introduction.

The introduction should define the topic and purpose of the review and describe its relevance to family practice. The traditional way of doing this is to discuss the epidemiology of the condition, stating how many people have it at one point in time (prevalence) or what percentage of the population is expected to develop it over a given period of time (incidence). A more engaging way of doing this is to indicate how often a typical family physician is likely to encounter this problem during a week, month, year, or career. Emphasize the key CME objectives of the review and summarize them in a separate table entitled “CME Objectives.”

The methods section should briefly indicate how the literature search was conducted and what major sources of evidence were used. Ideally, indicate what predetermined criteria were used to include or exclude studies (e.g., studies had to be independently rated as being high quality by an established evaluation process, such as the Cochrane Collaboration). Be comprehensive in trying to identify all major relevant research. Critically evaluate the quality of research reviewed. Avoid selective referencing of only information that supports your conclusions. If there is controversy on a topic, address the full scope of the controversy.

The discussion can then follow the typical format of a clinical review article. It should touch on one or more of the following subtopics: etiology, pathophysiology, clinical presentation (signs and symptoms), diagnostic evaluation (history, physical examination, laboratory evaluation, and diagnostic imaging), differential diagnosis, treatment (goals, medical/surgical therapy, laboratory testing, patient education, and follow-up), prognosis, prevention, and future directions.

The review will be comprehensive and balanced if it acknowledges controversies, unresolved questions, recent developments, other viewpoints, and any apparent conflicts of interest or instances of bias that might affect the strength of the evidence presented. Emphasize an evidence-supported approach or, where little evidence exists, a consensus viewpoint. In the absence of a consensus viewpoint, you may describe generally accepted practices or discuss one or more reasoned approaches, but acknowledge that solid support for these recommendations is lacking.

In some cases, cost-effectiveness analyses may be important in deciding how to implement health care services, especially preventive services. 10 When relevant, mention high-quality cost-effectiveness analyses to help clarify the costs and health benefits associated with alternative interventions to achieve a given health outcome. Highlight key points about diagnosis and treatment in the discussion and include a summary table of the key take-home points. These points are not necessarily the same as the key recommendations, whose level of evidence is rated, although some of them will be.

Use tables, figures, and illustrations to highlight key points, and present a step-wise, algorithmic approach to diagnosis or treatment when possible.

Rate the evidence for key statements, especially treatment recommendations. We expect that most articles will have at most two to four key statements; some will have none. Rate only those statements that have corresponding references and base the rating on the quality and level of evidence presented in the supporting citations. Use primary sources (original research, RCTs, meta-analyses, and systematic reviews) as the basis for determining the level of evidence. In other words, the supporting citation should be a primary research source of the information, not a secondary source (such as a nonsystematic review article or a textbook) that simply cites the original source. Systematic reviews that analyze multiple RCTs are good sources for determining ratings of evidence.

The references should include the most current and important sources of support for key statements (i.e., studies referred to, new information, controversial material, specific quantitative data, and information that would not usually be found in most general reference textbooks). Generally, these references will be key evidence-based recommendations, meta-analyses, or landmark articles. Although some journals publish exhaustive lists of reference citations, AFP prefers to include a succinct list of key references. (We will make more extensive reference lists available on our Web site or provide links to your personal reference list.)

You may use the following checklist to ensure the completeness of your evidence-based review article; use the source list of reviews to identify important sources of evidence-based medicine materials.

Checklist for an Evidence-Based Clinical Review Article

The topic is common in family practice, especially topics in which there is new, important information about diagnosis or treatment.

The introduction defines the topic and the purpose of the review, and describes its relevance to family practice.

A table of CME objectives for the review is included.

The review states how you did your literature search and indicates what sources you checked to ensure a comprehensive assessment of relevant studies (e.g., MEDLINE, the Cochrane Collaboration Database, the Center for Research Support, TRIP Database).

Several sources of evidence-based reviews on the topic are evaluated ( Table 1 ) .

Where possible, POEM (dealing with changes in morbidity, mortality, or quality of life) rather than DOE (dealing with mechanistic explanations or surrogate end points, such as changes in laboratory tests) is used to support key clinical recommendations ( Table 2 ) .

Studies of patients likely to be representative of those in primary care practices, rather than subspecialty referral centers, are emphasized.

Studies that are not only statistically significant but also clinically significant are emphasized; e.g., interventions with meaningful changes in absolute risk reduction and low numbers needed to treat. (See http://www.cebm.net/index.aspx?o=1116 .) 11

The level of evidence for key clinical recommendations is labeled using the following rating scale: level A (RCT/meta-analysis), level B (other evidence), and level C (consensus/expert opinion).

Acknowledge controversies, recent developments, other viewpoints, and any apparent conflicts of interest or instances of bias that might affect the strength of the evidence presented.

Highlight key points about diagnosis and treatment in the discussion and include a summary table of key take-home points.

Use tables, figures, and illustrations to highlight key points and present a step-wise, algorithmic approach to diagnosis or treatment when possible.

Emphasize evidence-based guidelines and primary research studies, rather than other review articles, unless they are systematic reviews.

The essential elements of this checklist are summarized in Table 3 .

Siwek J. Reading and evaluating clinical review articles. Am Fam Physician. 1997;55:2064-2069.

Shaughnessy AF, Slawson DC. Getting the most from review articles: a guide for readers and writers. Am Fam Physician. 1997;55:2155-60.

Pitt B, Zannad F, Remme WJ, Cody R, Castaigne A, Perez A, et al. The effect of spironolactone on morbidity and mortality in patients with severe heart failure. N Engl J Med. 1999;341:709-17.

Flynn CA, D'Amico F, Smith G. Should we patch corneal abrasions? A meta-analysis. J Fam Pract. 1998;47:264-70.

Slawson DC, Shaughnessy AF, Bennett JH. Becoming a medical information master: feeling good about not knowing everything. J Fam Pract. 1994;38:505-13.

Shaughnessy AF, Slawson DC, Bennett JH. Becoming an information master: a guidebook to the medical information jungle. J Fam Pract. 1994;39:489-99.

Slawson DC, Shaughnessy AF. Becoming an information master: using POEMs to change practice with confidence. Patient-oriented evidence that matters. J Fam Pract. 2000;49:63-7.

Harris RP, Helfand M, Woolf SH, Lohr KN, Mulrow CD, Teutsch SM, et al. Methods Work Group, Third U.S. Preventive Services Task Force. Current methods of the U.S. Preventive Services Task Force. A review of the process. Am J Prev Med. 2001;20(3 suppl):21-35.

CATbank topics: levels of evidence and grades of recommendations. Retrieved November 2001, from: http://www.cebm.net/ .

Saha S, Hoerger TJ, Pignone MP, Teutsch SM, Helfand M, Mandelblatt JS. for the Cost Work Group of the Third U.S. Preventive Services Task Force. The art and science of incorporating cost effectiveness into evidence-based recommendations for clinical preventive services. Am J Prev Med. 2001;20(3 suppl):36-43.

Evidence-based medicine glossary. Retrieved November 2001, from: http://www.cebm.net/index.aspx?o=1116 .

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Writing in the Health Sciences: Research and Lit Reviews

• Research and Lit Reviews
• Tables and Figures
• Citation Management
• Further Reference

What Is a Literature Review?

In simple terms, a literature review investigates the available information on a certain topic. It may be only a knowledge survey with an intentional focus. However, it is often a well-organized examination of the existing research which evaluates each resource in a systematic way. Often a lit review will involve a series of inclusion/exclusion criteria or an assessment rubric which examines the research in-depth. Below are some interesting sources to consider.

The Writing Center's Literature Reviews - UNC-Chapel Hill's writing center explains some of the key criteria involved in doing a literature review.

Literature Review vs. Systematic Review - This recent article details the difference between a literature review and a systematic review. Though the two share similar attributes, key differences are identified here.

Literature Review Steps

1. Identify a research question. For example: "Does the use of warfarin in elderly patients recovering from myocardial infarction help prevent stroke?"

2. Consider which databases might provide information for your topic. Often PubMed or CINAHL will cover a wide spectrum of biomedical issues. However, other databases and grey literature sources may specialize in certain disciplines. Embase is generally comprehensive but also specializes in pharmacological interventions.

3. Select the major subjects or ideas from your question.  Focus in on the particular concepts involved in your research. Then brainstorm synonyms and related terminology for these topics.

4. Look for the  preferred indexing terms for each concept in your question. This is especially important with databases such as PubMed, CINAHL, or Scopus where headings within the MeSH database or under the Emtree umbrella are present.  For example, the above question's keywords such as " warfarin " or "myocardial infarction" can involve related terminology or subject headings such as "anti-coagulants" or "cardiovascular disease."

5. Build your search using boolean operators. Combine the synonyms in your database using boolean operators such as AND or OR. Sometimes it is necessary to research parts of a question rather than the whole. So you might link searches for things like the preventive effects of anti-coagulants with stroke or embolism, then AND these results with the therapy for patients with cardiovascular disease.

6. Filter and save your search results from the first database (do this for all databases). This may be a short list because of your topic's limitations, but it should be no longer than 15 articles for an initial search. Make sure your list is saved or archived and presents you with what's needed to access the full text.

7. Use the same process with the next databases on your list. But pay attention to how certain major headings may alter the terminology. "Stroke" may have a suggested term of "embolism" or even "cerebrovascular incident" depending on the database.

8. Read through the material for inclusion/exclusion . Based on your project's criteria and objective, consider which studies or reviews deserve to be included and which should be discarded. Make sure the information you have permits you to go forward. 

9. Write the literature review. Begin by summarizing why your research is important and explain why your approach will help fill gaps in current knowledge. Then incorporate how the information you've selected will help you to do this. You do not need to write about all of the included research you've chosen, only the most pe rtinent.

10. Select the most relevant literature for inclusion in the body of your report. Choose the articles and data sets that are most particularly relevant to your experimental approach. Consider how you might arrange these sources in the body of your draft. 

Library Books

Call #: WZ 345 G192h 2011

ISBN #: 9780763771867

This book details a practical, step-by-step method for conducting a literature review in the health sciences. Aiming to  synthesize the information while also analyzing it, the Matrix Indexing System enables users to establish a  structured process for tracking, organizing and integrating the knowledge within a collection.

Key Research Databases

PubMed -  The premier medical database for review articles in medicine, nursing, healthcare, other related biomedical disciplines. PubMed contains over 20 million citations and can be navigated through multiple database capabilities and searching strategies.

CINAHL Ultimate - Offers comprehensive coverage of health science literature. CINAHL is particularly useful for those researching the allied disciplines of nursing, medicine, and pharmaceutical sciences.

Scopus - Database with over 12 million abstracts and citations which include peer-reviewed titles from international and Open Access journals. Also includes interactive bibliometrics and researcher profiling.

Embase - Elsevier's fully interoperable database of both Medline and Emtree-indexed articles. Embase also specializes in pharmacologic interventions.

Cochrane - Selected evidence-based medicine resources from the Cochrane Collaboration that includes peer-reviewed systematic reviews and randomized controlled trials. Access this database through OVID with TTUHSC Libraries.

DARE - Literally the Datatase of Abstracts of Reviews of Effectiveness, this collection of systematic reviews and other evidence-based research contains critical assessments from a wide variety of medical journals.

TRIP - This TRIP database is structured according to the level of evidence for its EBM content. It allows users to quickly and easily locate high-quality, accredited medical literature for clinical and research purposes.

Web of Science - Contains bibliographic articles and data from a wide variety of publications in the life sciences and other fields. Also, see this link for conducting a lit review exclusively within Web of Science.

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Literature review

Literature reviews are a way of identifying what is already known about a research area and what the gaps are. To do a literature review, you will need to identify relevant literature, often through searching academic databases, and then review existing literature. Most often, you will do the literature review at the beginning of your research project, but it is iterative, so you may choose to change the literature review as you move through your project.

Searching the literature

The University of Melbourne Library has some resources about searching the literature. Leonie spoke about how she met with a librarian about searching the literature. You may also want to meet face-to-face with a librarian or attend a class at the library to learn more about literature searching. When you search the literature, you may find journal articles, reports, books and other materials.

Filing, categorising and managing literature

In order to manage the literature you have identified through searches, you may choose to use a reference manager. The University of Melbourne has access to RefWorks and Endnote. Further information about accessing this software is available through the University of Melbourne Library .

Writing a literature review

The purpose of the literature review is to identify what is already known about a particular research area and critically analyse prior studies. It will also help you to identify any gaps in the research and situate your research in what is already known about a particular topic.

• Aveyard, H. (2010). Doing a literature review in health and social care: A practical guide . London, UK: McGraw-Hill Education. Retrieved from Proquest https://ebookcentral.proquest.com/lib/unimelb/detail.action?docID=771406
• Reeves, S., Koppel, I., Barr, H., Freeth, D., Hammick, M. (2002). Twelve tips for undertaking a systematic review. Medical Teacher . 24(4), 358-363 .
• Grant, M.J. and Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal .
• Jesson, J., & Lacey, F. (2006). How to do (or not to do) a critical literature review. Pharmacy Education , 6(2), 139-148 .
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• Volume 19, Issue 1
• Reviewing the literature
• Article Text
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• Joanna Smith 1 ,
• Helen Noble 2
• 1 School of Healthcare, University of Leeds , Leeds , UK
• 2 School of Nursing and Midwifery, Queens's University Belfast , Belfast , UK
• Correspondence to Dr Joanna Smith , School of Healthcare, University of Leeds, Leeds LS2 9JT, UK; j.e.smith1{at}leeds.ac.uk

https://doi.org/10.1136/eb-2015-102252

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Implementing evidence into practice requires nurses to identify, critically appraise and synthesise research. This may require a comprehensive literature review: this article aims to outline the approaches and stages required and provides a working example of a published review.

Are there different approaches to undertaking a literature review?

What stages are required to undertake a literature review.

The rationale for the review should be established; consider why the review is important and relevant to patient care/safety or service delivery. For example, Noble et al 's 4 review sought to understand and make recommendations for practice and research in relation to dialysis refusal and withdrawal in patients with end-stage renal disease, an area of care previously poorly described. If appropriate, highlight relevant policies and theoretical perspectives that might guide the review. Once the key issues related to the topic, including the challenges encountered in clinical practice, have been identified formulate a clear question, and/or develop an aim and specific objectives. The type of review undertaken is influenced by the purpose of the review and resources available. However, the stages or methods used to undertake a review are similar across approaches and include:

Formulating clear inclusion and exclusion criteria, for example, patient groups, ages, conditions/treatments, sources of evidence/research designs;

Justifying data bases and years searched, and whether strategies including hand searching of journals, conference proceedings and research not indexed in data bases (grey literature) will be undertaken;

Developing search terms, the PICU (P: patient, problem or population; I: intervention; C: comparison; O: outcome) framework is a useful guide when developing search terms;

Developing search skills (eg, understanding Boolean Operators, in particular the use of AND/OR) and knowledge of how data bases index topics (eg, MeSH headings). Working with a librarian experienced in undertaking health searches is invaluable when developing a search.

Once studies are selected, the quality of the research/evidence requires evaluation. Using a quality appraisal tool, such as the Critical Appraisal Skills Programme (CASP) tools, 5 results in a structured approach to assessing the rigour of studies being reviewed. 3 Approaches to data synthesis for quantitative studies may include a meta-analysis (statistical analysis of data from multiple studies of similar designs that have addressed the same question), or findings can be reported descriptively. 6 Methods applicable for synthesising qualitative studies include meta-ethnography (themes and concepts from different studies are explored and brought together using approaches similar to qualitative data analysis methods), narrative summary, thematic analysis and content analysis. 7 Table 1 outlines the stages undertaken for a published review that summarised research about parents’ experiences of living with a child with a long-term condition. 8

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An example of rapid evidence assessment review

In summary, the type of literature review depends on the review purpose. For the novice reviewer undertaking a review can be a daunting and complex process; by following the stages outlined and being systematic a robust review is achievable. The importance of literature reviews should not be underestimated—they help summarise and make sense of an increasingly vast body of research promoting best evidence-based practice.

• ↵ Centre for Reviews and Dissemination . Guidance for undertaking reviews in health care . 3rd edn . York : CRD, York University , 2009 .
• ↵ Canadian Best Practices Portal. http://cbpp-pcpe.phac-aspc.gc.ca/interventions/selected-systematic-review-sites / ( accessed 7.8.2015 ).
• Bridges J , et al
• ↵ Critical Appraisal Skills Programme (CASP). http://www.casp-uk.net / ( accessed 7.8.2015 ).
• Dixon-Woods M ,
• Shaw R , et al
• Agarwal S ,
• Jones D , et al
• Cheater F ,

Twitter Follow Joanna Smith at @josmith175

Competing interests None declared.

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How to Conduct a Literature Review (Health Sciences and Beyond)

• What is a Literature Review?
• Developing a Research Question
• Selection Criteria
• Database Search
• Documenting Your Search

Review Matrix

• Reference Management

Using a spreadsheet or table to organize the key elements (e.g. subjects, methodologies, results) of articles/books you plan to use in your literature review can be helpful. This is called a review matrix.

When you create a review matrix, the first few columns should include (1) the authors, title, journal, (2) publication year, and (3) purpose of the paper. The remaining columns should identify important aspects of each study such as methodology and findings.

Click on the image below to view a sample review matrix.

You can also download this template as a Microsoft Excel file .

The information on this page is from the book below. The 5th edition is available online through VCU Libraries.

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How to write a review article?

In the medical sciences, the importance of review articles is rising. When clinicians want to update their knowledge and generate guidelines about a topic, they frequently use reviews as a starting point. The value of a review is associated with what has been done, what has been found and how these findings are presented. Before asking ‘how,’ the question of ‘why’ is more important when starting to write a review. The main and fundamental purpose of writing a review is to create a readable synthesis of the best resources available in the literature for an important research question or a current area of research. Although the idea of writing a review is attractive, it is important to spend time identifying the important questions. Good review methods are critical because they provide an unbiased point of view for the reader regarding the current literature. There is a consensus that a review should be written in a systematic fashion, a notion that is usually followed. In a systematic review with a focused question, the research methods must be clearly described. A ‘methodological filter’ is the best method for identifying the best working style for a research question, and this method reduces the workload when surveying the literature. An essential part of the review process is differentiating good research from bad and leaning on the results of the better studies. The ideal way to synthesize studies is to perform a meta-analysis. In conclusion, when writing a review, it is best to clearly focus on fixed ideas, to use a procedural and critical approach to the literature and to express your findings in an attractive way.

The importance of review articles in health sciences is increasing day by day. Clinicians frequently benefit from review articles to update their knowledge in their field of specialization, and use these articles as a starting point for formulating guidelines. [ 1 , 2 ] The institutions which provide financial support for further investigations resort to these reviews to reveal the need for these researches. [ 3 ] As is the case with all other researches, the value of a review article is related to what is achieved, what is found, and the way of communicating this information. A few studies have evaluated the quality of review articles. Murlow evaluated 50 review articles published in 1985, and 1986, and revealed that none of them had complied with clear-cut scientific criteria. [ 4 ] In 1996 an international group that analyzed articles, demonstrated the aspects of review articles, and meta-analyses that had not complied with scientific criteria, and elaborated QUOROM (QUality Of Reporting Of Meta-analyses) statement which focused on meta-analyses of randomized controlled studies. [ 5 ] Later on this guideline was updated, and named as PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). [ 6 ]

Review articles are divided into 2 categories as narrative, and systematic reviews. Narrative reviews are written in an easily readable format, and allow consideration of the subject matter within a large spectrum. However in a systematic review, a very detailed, and comprehensive literature surveying is performed on the selected topic. [ 7 , 8 ] Since it is a result of a more detailed literature surveying with relatively lesser involvement of author’s bias, systematic reviews are considered as gold standard articles. Systematic reviews can be diivded into qualitative, and quantitative reviews. In both of them detailed literature surveying is performed. However in quantitative reviews, study data are collected, and statistically evaluated (ie. meta-analysis). [ 8 ]

Before inquring for the method of preparation of a review article, it is more logical to investigate the motivation behind writing the review article in question. The fundamental rationale of writing a review article is to make a readable synthesis of the best literature sources on an important research inquiry or a topic. This simple definition of a review article contains the following key elements:

• The question(s) to be dealt with
• Methods used to find out, and select the best quality researches so as to respond to these questions.
• To synthetize available, but quite different researches

For the specification of important questions to be answered, number of literature references to be consulted should be more or less determined. Discussions should be conducted with colleagues in the same area of interest, and time should be reserved for the solution of the problem(s). Though starting to write the review article promptly seems to be very alluring, the time you spend for the determination of important issues won’t be a waste of time. [ 9 ]

The PRISMA statement [ 6 ] elaborated to write a well-designed review articles contains a 27-item checklist ( Table 1 ). It will be reasonable to fulfill the requirements of these items during preparation of a review article or a meta-analysis. Thus preparation of a comprehensible article with a high-quality scientific content can be feasible.

PRISMA statement: A 27-item checklist

Contents and format

Important differences exist between systematic, and non-systematic reviews which especially arise from methodologies used in the description of the literature sources. A non-systematic review means use of articles collected for years with the recommendations of your colleagues, while systematic review is based on struggles to search for, and find the best possible researches which will respond to the questions predetermined at the start of the review.

Though a consensus has been reached about the systematic design of the review articles, studies revealed that most of them had not been written in a systematic format. McAlister et al. analyzed review articles in 6 medical journals, and disclosed that in less than one fourth of the review articles, methods of description, evaluation or synthesis of evidence had been provided, one third of them had focused on a clinical topic, and only half of them had provided quantitative data about the extend of the potential benefits. [ 10 ]

Use of proper methodologies in review articles is important in that readers assume an objective attitude towards updated information. We can confront two problems while we are using data from researches in order to answer certain questions. Firstly, we can be prejudiced during selection of research articles or these articles might be biased. To minimize this risk, methodologies used in our reviews should allow us to define, and use researches with minimal degree of bias. The second problem is that, most of the researches have been performed with small sample sizes. In statistical methods in meta-analyses, available researches are combined to increase the statistical power of the study. The problematic aspect of a non-systematic review is that our tendency to give biased responses to the questions, in other words we apt to select the studies with known or favourite results, rather than the best quality investigations among them.

As is the case with many research articles, general format of a systematic review on a single subject includes sections of Introduction, Methods, Results, and Discussion ( Table 2 ).

Structure of a systematic review

Preparation of the review article

Steps, and targets of constructing a good review article are listed in Table 3 . To write a good review article the items in Table 3 should be implemented step by step. [ 11 – 13 ]

Steps of a systematic review

The research question

It might be helpful to divide the research question into components. The most prevalently used format for questions related to the treatment is PICO (P - Patient, Problem or Population; I-Intervention; C-appropriate Comparisons, and O-Outcome measures) procedure. For example In female patients (P) with stress urinary incontinence, comparisons (C) between transobturator, and retropubic midurethral tension-free band surgery (I) as for patients’ satisfaction (O).

Finding Studies

In a systematic review on a focused question, methods of investigation used should be clearly specified.

Ideally, research methods, investigated databases, and key words should be described in the final report. Different databases are used dependent on the topic analyzed. In most of the clinical topics, Medline should be surveyed. However searching through Embase and CINAHL can be also appropriate.

While determining appropriate terms for surveying, PICO elements of the issue to be sought may guide the process. Since in general we are interested in more than one outcome, P, and I can be key elements. In this case we should think about synonyms of P, and I elements, and combine them with a conjunction AND.

One method which might alleviate the workload of surveying process is “methodological filter” which aims to find the best investigation method for each research question. A good example of this method can be found in PubMed interface of Medline. The Clinical Queries tool offers empirically developed filters for five different inquiries as guidelines for etiology, diagnosis, treatment, prognosis or clinical prediction.

Evaluation of the Quality of the Study

As an indispensable component of the review process is to discriminate good, and bad quality researches from each other, and the outcomes should be based on better qualified researches, as far as possible. To achieve this goal you should know the best possible evidence for each type of question The first component of the quality is its general planning/design of the study. General planning/design of a cohort study, a case series or normal study demonstrates variations.

A hierarchy of evidence for different research questions is presented in Table 4 . However this hierarchy is only a first step. After you find good quality research articles, you won’t need to read all the rest of other articles which saves you tons of time. [ 14 ]

Determination of levels of evidence based on the type of the research question

Formulating a Synthesis

Rarely all researches arrive at the same conclusion. In this case a solution should be found. However it is risky to make a decision based on the votes of absolute majority. Indeed, a well-performed large scale study, and a weakly designed one are weighed on the same scale. Therefore, ideally a meta-analysis should be performed to solve apparent differences. Ideally, first of all, one should be focused on the largest, and higher quality study, then other studies should be compared with this basic study.

Conclusions

In conclusion, during writing process of a review article, the procedures to be achieved can be indicated as follows: 1) Get rid of fixed ideas, and obsessions from your head, and view the subject from a large perspective. 2) Research articles in the literature should be approached with a methodological, and critical attitude and 3) finally data should be explained in an attractive way.