characteristics of case study method pdf

From David E. Gray \(2014\). Doing Research in the Real World \(3rd ed.\) London, UK: Sage.

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Continuing to enhance the quality of case study methodology in health services research

Shannon l. sibbald.

1 Faculty of Health Sciences, Western University, London, Ontario, Canada.

2 Department of Family Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

3 The Schulich Interfaculty Program in Public Health, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

Stefan Paciocco

Meghan fournie, rachelle van asseldonk, tiffany scurr.

Case study methodology has grown in popularity within Health Services Research (HSR). However, its use and merit as a methodology are frequently criticized due to its flexible approach and inconsistent application. Nevertheless, case study methodology is well suited to HSR because it can track and examine complex relationships, contexts, and systems as they evolve. Applied appropriately, it can help generate information on how multiple forms of knowledge come together to inform decision-making within healthcare contexts. In this article, we aim to demystify case study methodology by outlining its philosophical underpinnings and three foundational approaches. We provide literature-based guidance to decision-makers, policy-makers, and health leaders on how to engage in and critically appraise case study design. We advocate that researchers work in collaboration with health leaders to detail their research process with an aim of strengthening the validity and integrity of case study for its continued and advanced use in HSR.

Introduction

The popularity of case study research methodology in Health Services Research (HSR) has grown over the past 40 years. 1 This may be attributed to a shift towards the use of implementation research and a newfound appreciation of contextual factors affecting the uptake of evidence-based interventions within diverse settings. 2 Incorporating context-specific information on the delivery and implementation of programs can increase the likelihood of success. 3 , 4 Case study methodology is particularly well suited for implementation research in health services because it can provide insight into the nuances of diverse contexts. 5 , 6 In 1999, Yin 7 published a paper on how to enhance the quality of case study in HSR, which was foundational for the emergence of case study in this field. Yin 7 maintains case study is an appropriate methodology in HSR because health systems are constantly evolving, and the multiple affiliations and diverse motivations are difficult to track and understand with traditional linear methodologies.

Despite its increased popularity, there is debate whether a case study is a methodology (ie, a principle or process that guides research) or a method (ie, a tool to answer research questions). Some criticize case study for its high level of flexibility, perceiving it as less rigorous, and maintain that it generates inadequate results. 8 Others have noted issues with quality and consistency in how case studies are conducted and reported. 9 Reporting is often varied and inconsistent, using a mix of approaches such as case reports, case findings, and/or case study. Authors sometimes use incongruent methods of data collection and analysis or use the case study as a default when other methodologies do not fit. 9 , 10 Despite these criticisms, case study methodology is becoming more common as a viable approach for HSR. 11 An abundance of articles and textbooks are available to guide researchers through case study research, including field-specific resources for business, 12 , 13 nursing, 14 and family medicine. 15 However, there remains confusion and a lack of clarity on the key tenets of case study methodology.

Several common philosophical underpinnings have contributed to the development of case study research 1 which has led to different approaches to planning, data collection, and analysis. This presents challenges in assessing quality and rigour for researchers conducting case studies and stakeholders reading results.

This article discusses the various approaches and philosophical underpinnings to case study methodology. Our goal is to explain it in a way that provides guidance for decision-makers, policy-makers, and health leaders on how to understand, critically appraise, and engage in case study research and design, as such guidance is largely absent in the literature. This article is by no means exhaustive or authoritative. Instead, we aim to provide guidance and encourage dialogue around case study methodology, facilitating critical thinking around the variety of approaches and ways quality and rigour can be bolstered for its use within HSR.

Purpose of case study methodology

Case study methodology is often used to develop an in-depth, holistic understanding of a specific phenomenon within a specified context. 11 It focuses on studying one or multiple cases over time and uses an in-depth analysis of multiple information sources. 16 , 17 It is ideal for situations including, but not limited to, exploring under-researched and real-life phenomena, 18 especially when the contexts are complex and the researcher has little control over the phenomena. 19 , 20 Case studies can be useful when researchers want to understand how interventions are implemented in different contexts, and how context shapes the phenomenon of interest.

In addition to demonstrating coherency with the type of questions case study is suited to answer, there are four key tenets to case study methodologies: (1) be transparent in the paradigmatic and theoretical perspectives influencing study design; (2) clearly define the case and phenomenon of interest; (3) clearly define and justify the type of case study design; and (4) use multiple data collection sources and analysis methods to present the findings in ways that are consistent with the methodology and the study’s paradigmatic base. 9 , 16 The goal is to appropriately match the methods to empirical questions and issues and not to universally advocate any single approach for all problems. 21

Approaches to case study methodology

Three authors propose distinct foundational approaches to case study methodology positioned within different paradigms: Yin, 19 , 22 Stake, 5 , 23 and Merriam 24 , 25 ( Table 1 ). Yin is strongly post-positivist whereas Stake and Merriam are grounded in a constructivist paradigm. Researchers should locate their research within a paradigm that explains the philosophies guiding their research 26 and adhere to the underlying paradigmatic assumptions and key tenets of the appropriate author’s methodology. This will enhance the consistency and coherency of the methods and findings. However, researchers often do not report their paradigmatic position, nor do they adhere to one approach. 9 Although deliberately blending methodologies may be defensible and methodologically appropriate, more often it is done in an ad hoc and haphazard way, without consideration for limitations.

Cross-analysis of three case study approaches, adapted from Yazan 2015

The post-positive paradigm postulates there is one reality that can be objectively described and understood by “bracketing” oneself from the research to remove prejudice or bias. 27 Yin focuses on general explanation and prediction, emphasizing the formulation of propositions, akin to hypothesis testing. This approach is best suited for structured and objective data collection 9 , 11 and is often used for mixed-method studies.

Constructivism assumes that the phenomenon of interest is constructed and influenced by local contexts, including the interaction between researchers, individuals, and their environment. 27 It acknowledges multiple interpretations of reality 24 constructed within the context by the researcher and participants which are unlikely to be replicated, should either change. 5 , 20 Stake and Merriam’s constructivist approaches emphasize a story-like rendering of a problem and an iterative process of constructing the case study. 7 This stance values researcher reflexivity and transparency, 28 acknowledging how researchers’ experiences and disciplinary lenses influence their assumptions and beliefs about the nature of the phenomenon and development of the findings.

Defining a case

A key tenet of case study methodology often underemphasized in literature is the importance of defining the case and phenomenon. Researches should clearly describe the case with sufficient detail to allow readers to fully understand the setting and context and determine applicability. Trying to answer a question that is too broad often leads to an unclear definition of the case and phenomenon. 20 Cases should therefore be bound by time and place to ensure rigor and feasibility. 6

Yin 22 defines a case as “a contemporary phenomenon within its real-life context,” (p13) which may contain a single unit of analysis, including individuals, programs, corporations, or clinics 29 (holistic), or be broken into sub-units of analysis, such as projects, meetings, roles, or locations within the case (embedded). 30 Merriam 24 and Stake 5 similarly define a case as a single unit studied within a bounded system. Stake 5 , 23 suggests bounding cases by contexts and experiences where the phenomenon of interest can be a program, process, or experience. However, the line between the case and phenomenon can become muddy. For guidance, Stake 5 , 23 describes the case as the noun or entity and the phenomenon of interest as the verb, functioning, or activity of the case.

Designing the case study approach

Yin’s approach to a case study is rooted in a formal proposition or theory which guides the case and is used to test the outcome. 1 Stake 5 advocates for a flexible design and explicitly states that data collection and analysis may commence at any point. Merriam’s 24 approach blends both Yin and Stake’s, allowing the necessary flexibility in data collection and analysis to meet the needs.

Yin 30 proposed three types of case study approaches—descriptive, explanatory, and exploratory. Each can be designed around single or multiple cases, creating six basic case study methodologies. Descriptive studies provide a rich description of the phenomenon within its context, which can be helpful in developing theories. To test a theory or determine cause and effect relationships, researchers can use an explanatory design. An exploratory model is typically used in the pilot-test phase to develop propositions (eg, Sibbald et al. 31 used this approach to explore interprofessional network complexity). Despite having distinct characteristics, the boundaries between case study types are flexible with significant overlap. 30 Each has five key components: (1) research question; (2) proposition; (3) unit of analysis; (4) logical linking that connects the theory with proposition; and (5) criteria for analyzing findings.

Contrary to Yin, Stake 5 believes the research process cannot be planned in its entirety because research evolves as it is performed. Consequently, researchers can adjust the design of their methods even after data collection has begun. Stake 5 classifies case studies into three categories: intrinsic, instrumental, and collective/multiple. Intrinsic case studies focus on gaining a better understanding of the case. These are often undertaken when the researcher has an interest in a specific case. Instrumental case study is used when the case itself is not of the utmost importance, and the issue or phenomenon (ie, the research question) being explored becomes the focus instead (eg, Paciocco 32 used an instrumental case study to evaluate the implementation of a chronic disease management program). 5 Collective designs are rooted in an instrumental case study and include multiple cases to gain an in-depth understanding of the complexity and particularity of a phenomenon across diverse contexts. 5 , 23 In collective designs, studying similarities and differences between the cases allows the phenomenon to be understood more intimately (for examples of this in the field, see van Zelm et al. 33 and Burrows et al. 34 In addition, Sibbald et al. 35 present an example where a cross-case analysis method is used to compare instrumental cases).

Merriam’s approach is flexible (similar to Stake) as well as stepwise and linear (similar to Yin). She advocates for conducting a literature review before designing the study to better understand the theoretical underpinnings. 24 , 25 Unlike Stake or Yin, Merriam proposes a step-by-step guide for researchers to design a case study. These steps include performing a literature review, creating a theoretical framework, identifying the problem, creating and refining the research question(s), and selecting a study sample that fits the question(s). 24 , 25 , 36

Data collection and analysis

Using multiple data collection methods is a key characteristic of all case study methodology; it enhances the credibility of the findings by allowing different facets and views of the phenomenon to be explored. 23 Common methods include interviews, focus groups, observation, and document analysis. 5 , 37 By seeking patterns within and across data sources, a thick description of the case can be generated to support a greater understanding and interpretation of the whole phenomenon. 5 , 17 , 20 , 23 This technique is called triangulation and is used to explore cases with greater accuracy. 5 Although Stake 5 maintains case study is most often used in qualitative research, Yin 17 supports a mix of both quantitative and qualitative methods to triangulate data. This deliberate convergence of data sources (or mixed methods) allows researchers to find greater depth in their analysis and develop converging lines of inquiry. For example, case studies evaluating interventions commonly use qualitative interviews to describe the implementation process, barriers, and facilitators paired with a quantitative survey of comparative outcomes and effectiveness. 33 , 38 , 39

Yin 30 describes analysis as dependent on the chosen approach, whether it be (1) deductive and rely on theoretical propositions; (2) inductive and analyze data from the “ground up”; (3) organized to create a case description; or (4) used to examine plausible rival explanations. According to Yin’s 40 approach to descriptive case studies, carefully considering theory development is an important part of study design. “Theory” refers to field-relevant propositions, commonly agreed upon assumptions, or fully developed theories. 40 Stake 5 advocates for using the researcher’s intuition and impression to guide analysis through a categorical aggregation and direct interpretation. Merriam 24 uses six different methods to guide the “process of making meaning” (p178) : (1) ethnographic analysis; (2) narrative analysis; (3) phenomenological analysis; (4) constant comparative method; (5) content analysis; and (6) analytic induction.

Drawing upon a theoretical or conceptual framework to inform analysis improves the quality of case study and avoids the risk of description without meaning. 18 Using Stake’s 5 approach, researchers rely on protocols and previous knowledge to help make sense of new ideas; theory can guide the research and assist researchers in understanding how new information fits into existing knowledge.

Practical applications of case study research

Columbia University has recently demonstrated how case studies can help train future health leaders. 41 Case studies encompass components of systems thinking—considering connections and interactions between components of a system, alongside the implications and consequences of those relationships—to equip health leaders with tools to tackle global health issues. 41 Greenwood 42 evaluated Indigenous peoples’ relationship with the healthcare system in British Columbia and used a case study to challenge and educate health leaders across the country to enhance culturally sensitive health service environments.

An important but often omitted step in case study research is an assessment of quality and rigour. We recommend using a framework or set of criteria to assess the rigour of the qualitative research. Suitable resources include Caelli et al., 43 Houghten et al., 44 Ravenek and Rudman, 45 and Tracy. 46

New directions in case study

Although “pragmatic” case studies (ie, utilizing practical and applicable methods) have existed within psychotherapy for some time, 47 , 48 only recently has the applicability of pragmatism as an underlying paradigmatic perspective been considered in HSR. 49 This is marked by uptake of pragmatism in Randomized Control Trials, recognizing that “gold standard” testing conditions do not reflect the reality of clinical settings 50 , 51 nor do a handful of epistemologically guided methodologies suit every research inquiry.

Pragmatism positions the research question as the basis for methodological choices, rather than a theory or epistemology, allowing researchers to pursue the most practical approach to understanding a problem or discovering an actionable solution. 52 Mixed methods are commonly used to create a deeper understanding of the case through converging qualitative and quantitative data. 52 Pragmatic case study is suited to HSR because its flexibility throughout the research process accommodates complexity, ever-changing systems, and disruptions to research plans. 49 , 50 Much like case study, pragmatism has been criticized for its flexibility and use when other approaches are seemingly ill-fit. 53 , 54 Similarly, authors argue that this results from a lack of investigation and proper application rather than a reflection of validity, legitimizing the need for more exploration and conversation among researchers and practitioners. 55

Although occasionally misunderstood as a less rigourous research methodology, 8 case study research is highly flexible and allows for contextual nuances. 5 , 6 Its use is valuable when the researcher desires a thorough understanding of a phenomenon or case bound by context. 11 If needed, multiple similar cases can be studied simultaneously, or one case within another. 16 , 17 There are currently three main approaches to case study, 5 , 17 , 24 each with their own definitions of a case, ontological and epistemological paradigms, methodologies, and data collection and analysis procedures. 37

Individuals’ experiences within health systems are influenced heavily by contextual factors, participant experience, and intricate relationships between different organizations and actors. 55 Case study research is well suited for HSR because it can track and examine these complex relationships and systems as they evolve over time. 6 , 7 It is important that researchers and health leaders using this methodology understand its key tenets and how to conduct a proper case study. Although there are many examples of case study in action, they are often under-reported and, when reported, not rigorously conducted. 9 Thus, decision-makers and health leaders should use these examples with caution. The proper reporting of case studies is necessary to bolster their credibility in HSR literature and provide readers sufficient information to critically assess the methodology. We also call on health leaders who frequently use case studies 56 – 58 to report them in the primary research literature.

The purpose of this article is to advocate for the continued and advanced use of case study in HSR and to provide literature-based guidance for decision-makers, policy-makers, and health leaders on how to engage in, read, and interpret findings from case study research. As health systems progress and evolve, the application of case study research will continue to increase as researchers and health leaders aim to capture the inherent complexities, nuances, and contextual factors. 7

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Case Method Teaching and Learning

What is the case method? How can the case method be used to engage learners? What are some strategies for getting started? This guide helps instructors answer these questions by providing an overview of the case method while highlighting learner-centered and digitally-enhanced approaches to teaching with the case method. The guide also offers tips to instructors as they get started with the case method and additional references and resources.

On this page:

What is case method teaching.

• Case Method at Columbia

Why use the Case Method?

Case method teaching approaches, how do i get started.

• Additional Resources

The CTL is here to help!

For support with implementing a case method approach in your course, email [email protected] to schedule your 1-1 consultation .

Cite this resource: Columbia Center for Teaching and Learning (2019). Case Method Teaching and Learning. Columbia University. Retrieved from [today’s date] from https://ctl.columbia.edu/resources-and-technology/resources/case-method/  

Case method 1 teaching is an active form of instruction that focuses on a case and involves students learning by doing 2 3 . Cases are real or invented stories 4  that include “an educational message” or recount events, problems, dilemmas, theoretical or conceptual issue that requires analysis and/or decision-making.

Case-based teaching simulates real world situations and asks students to actively grapple with complex problems 5 6 This method of instruction is used across disciplines to promote learning, and is common in law, business, medicine, among other fields. See Table 1 below for a few types of cases and the learning they promote.

Table 1: Types of cases and the learning they promote.

For a more complete list, see Case Types & Teaching Methods: A Classification Scheme from the National Center for Case Study Teaching in Science.

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Case Method Teaching and Learning at Columbia

The case method is actively used in classrooms across Columbia, at the Morningside campus in the School of International and Public Affairs (SIPA), the School of Business, Arts and Sciences, among others, and at Columbia University Irving Medical campus.

Faculty Spotlight:

Professor Mary Ann Price on Using Case Study Method to Place Pre-Med Students in Real-Life Scenarios

Read more  

Professor De Pinho on Using the Case Method in the Mailman Core

Case method teaching has been found to improve student learning, to increase students’ perception of learning gains, and to meet learning objectives 8 9 . Faculty have noted the instructional benefits of cases including greater student engagement in their learning 10 , deeper student understanding of concepts, stronger critical thinking skills, and an ability to make connections across content areas and view an issue from multiple perspectives 11 . 

Through case-based learning, students are the ones asking questions about the case, doing the problem-solving, interacting with and learning from their peers, “unpacking” the case, analyzing the case, and summarizing the case. They learn how to work with limited information and ambiguity, think in professional or disciplinary ways, and ask themselves “what would I do if I were in this specific situation?”

The case method bridges theory to practice, and promotes the development of skills including: communication, active listening, critical thinking, decision-making, and metacognitive skills 12 , as students apply course content knowledge, reflect on what they know and their approach to analyzing, and make sense of a case. 

Though the case method has historical roots as an instructor-centered approach that uses the Socratic dialogue and cold-calling, it is possible to take a more learner-centered approach in which students take on roles and tasks traditionally left to the instructor. 

Cases are often used as “vehicles for classroom discussion” 13 . Students should be encouraged to take ownership of their learning from a case. Discussion-based approaches engage students in thinking and communicating about a case. Instructors can set up a case activity in which students are the ones doing the work of “asking questions, summarizing content, generating hypotheses, proposing theories, or offering critical analyses” 14 . 

The role of the instructor is to share a case or ask students to share or create a case to use in class, set expectations, provide instructions, and assign students roles in the discussion. Student roles in a case discussion can include: 

• discussion “starters” get the conversation started with a question or posing the questions that their peers came up with; 
• facilitators listen actively, validate the contributions of peers, ask follow-up questions, draw connections, refocus the conversation as needed; 
• recorders take-notes of the main points of the discussion, record on the board, upload to CourseWorks, or type and project on the screen; and 
• discussion “wrappers” lead a summary of the main points of the discussion. 

Prior to the case discussion, instructors can model case analysis and the types of questions students should ask, co-create discussion guidelines with students, and ask for students to submit discussion questions. During the discussion, the instructor can keep time, intervene as necessary (however the students should be doing the talking), and pause the discussion for a debrief and to ask students to reflect on what and how they learned from the case activity. 

Note: case discussions can be enhanced using technology. Live discussions can occur via video-conferencing (e.g., using Zoom ) or asynchronous discussions can occur using the Discussions tool in CourseWorks (Canvas) .

Table 2 includes a few interactive case method approaches. Regardless of the approach selected, it is important to create a learning environment in which students feel comfortable participating in a case activity and learning from one another. See below for tips on supporting student in how to learn from a case in the “getting started” section and how to create a supportive learning environment in the Guide for Inclusive Teaching at Columbia . 

Table 2. Strategies for Engaging Students in Case-Based Learning

Approaches to case teaching should be informed by course learning objectives, and can be adapted for small, large, hybrid, and online classes. Instructional technology can be used in various ways to deliver, facilitate, and assess the case method. For instance, an online module can be created in CourseWorks (Canvas) to structure the delivery of the case, allow students to work at their own pace, engage all learners, even those reluctant to speak up in class, and assess understanding of a case and student learning. Modules can include text, embedded media (e.g., using Panopto or Mediathread ) curated by the instructor, online discussion, and assessments. Students can be asked to read a case and/or watch a short video, respond to quiz questions and receive immediate feedback, post questions to a discussion, and share resources. 

For more information about options for incorporating educational technology to your course, please contact your Learning Designer .

To ensure that students are learning from the case approach, ask them to pause and reflect on what and how they learned from the case. Time to reflect  builds your students’ metacognition, and when these reflections are collected they provides you with insights about the effectiveness of your approach in promoting student learning.

Well designed case-based learning experiences: 1) motivate student involvement, 2) have students doing the work, 3) help students develop knowledge and skills, and 4) have students learning from each other.  

Designing a case-based learning experience should center around the learning objectives for a course. The following points focus on intentional design. 

Identify learning objectives, determine scope, and anticipate challenges. 

• Why use the case method in your course? How will it promote student learning differently than other approaches? 
• What are the learning objectives that need to be met by the case method? What knowledge should students apply and skills should they practice? 
• What is the scope of the case? (a brief activity in a single class session to a semester-long case-based course; if new to case method, start small with a single case). 
• What challenges do you anticipate (e.g., student preparation and prior experiences with case learning, discomfort with discussion, peer-to-peer learning, managing discussion) and how will you plan for these in your design? 
• If you are asking students to use transferable skills for the case method (e.g., teamwork, digital literacy) make them explicit. 

Determine how you will know if the learning objectives were met and develop a plan for evaluating the effectiveness of the case method to inform future case teaching. 

• What assessments and criteria will you use to evaluate student work or participation in case discussion? 
• How will you evaluate the effectiveness of the case method? What feedback will you collect from students? 
• How might you leverage technology for assessment purposes? For example, could you quiz students about the case online before class, accept assignment submissions online, use audience response systems (e.g., PollEverywhere) for formative assessment during class? 

Select an existing case, create your own, or encourage students to bring course-relevant cases, and prepare for its delivery

• Where will the case method fit into the course learning sequence? 
• Is the case at the appropriate level of complexity? Is it inclusive, culturally relevant, and relatable to students? 
• What materials and preparation will be needed to present the case to students? (e.g., readings, audiovisual materials, set up a module in CourseWorks). 

Plan for the case discussion and an active role for students

• What will your role be in facilitating case-based learning? How will you model case analysis for your students? (e.g., present a short case and demo your approach and the process of case learning) (Davis, 2009). 
• What discussion guidelines will you use that include your students’ input? 
• How will you encourage students to ask and answer questions, summarize their work, take notes, and debrief the case? 
• If students will be working in groups, how will groups form? What size will the groups be? What instructions will they be given? How will you ensure that everyone participates? What will they need to submit? Can technology be leveraged for any of these areas? 
• Have you considered students of varied cognitive and physical abilities and how they might participate in the activities/discussions, including those that involve technology? 

Student preparation and expectations

• How will you communicate about the case method approach to your students? When will you articulate the purpose of case-based learning and expectations of student engagement? What information about case-based learning and expectations will be included in the syllabus?
• What preparation and/or assignment(s) will students complete in order to learn from the case? (e.g., read the case prior to class, watch a case video prior to class, post to a CourseWorks discussion, submit a brief memo, complete a short writing assignment to check students’ understanding of a case, take on a specific role, prepare to present a critique during in-class discussion).

Andersen, E. and Schiano, B. (2014). Teaching with Cases: A Practical Guide . Harvard Business Press. 

Bonney, K. M. (2015). Case Study Teaching Method Improves Student Performance and Perceptions of Learning Gains†. Journal of Microbiology & Biology Education , 16 (1), 21–28. https://doi.org/10.1128/jmbe.v16i1.846

Davis, B.G. (2009). Chapter 24: Case Studies. In Tools for Teaching. Second Edition. Jossey-Bass. 

Garvin, D.A. (2003). Making the Case: Professional Education for the world of practice. Harvard Magazine. September-October 2003, Volume 106, Number 1, 56-107.

Golich, V.L. (2000). The ABCs of Case Teaching. International Studies Perspectives. 1, 11-29. 

Golich, V.L.; Boyer, M; Franko, P.; and Lamy, S. (2000). The ABCs of Case Teaching. Pew Case Studies in International Affairs. Institute for the Study of Diplomacy. 

Heath, J. (2015). Teaching & Writing Cases: A Practical Guide. The Case Center, UK. 

Herreid, C.F. (2011). Case Study Teaching. New Directions for Teaching and Learning. No. 128, Winder 2011, 31 – 40. 

Herreid, C.F. (2007). Start with a Story: The Case Study Method of Teaching College Science . National Science Teachers Association. Available as an ebook through Columbia Libraries. 

Herreid, C.F. (2006). “Clicker” Cases: Introducing Case Study Teaching Into Large Classrooms. Journal of College Science Teaching. Oct 2006, 36(2). https://search.proquest.com/docview/200323718?pq-origsite=gscholar  

Krain, M. (2016). Putting the Learning in Case Learning? The Effects of Case-Based Approaches on Student Knowledge, Attitudes, and Engagement. Journal on Excellence in College Teaching. 27(2), 131-153. 

Lundberg, K.O. (Ed.). (2011). Our Digital Future: Boardrooms and Newsrooms. Knight Case Studies Initiative. 

Popil, I. (2011). Promotion of critical thinking by using case studies as teaching method. Nurse Education Today, 31(2), 204–207. https://doi.org/10.1016/j.nedt.2010.06.002

Schiano, B. and Andersen, E. (2017). Teaching with Cases Online . Harvard Business Publishing. 

Thistlethwaite, JE; Davies, D.; Ekeocha, S.; Kidd, J.M.; MacDougall, C.; Matthews, P.; Purkis, J.; Clay D. (2012). The effectiveness of case-based learning in health professional education: A BEME systematic review . Medical Teacher. 2012; 34(6): e421-44. 

Yadav, A.; Lundeberg, M.; DeSchryver, M.; Dirkin, K.; Schiller, N.A.; Maier, K. and Herreid, C.F. (2007). Teaching Science with Case Studies: A National Survey of Faculty Perceptions of the Benefits and Challenges of Using Cases. Journal of College Science Teaching; Sept/Oct 2007; 37(1). 

Weimer, M. (2013). Learner-Centered Teaching: Five Key Changes to Practice. Second Edition. Jossey-Bass.

Additional resources 

Teaching with Cases , Harvard Kennedy School of Government. 

Features “what is a teaching case?” video that defines a teaching case, and provides documents to help students prepare for case learning, Common case teaching challenges and solutions, tips for teaching with cases. 

Promoting excellence and innovation in case method teaching: Teaching by the Case Method , Christensen Center for Teaching & Learning. Harvard Business School. 

National Center for Case Study Teaching in Science . University of Buffalo. 

A collection of peer-reviewed STEM cases to teach scientific concepts and content, promote process skills and critical thinking. The Center welcomes case submissions. Case classification scheme of case types and teaching methods:

• Different types of cases: analysis case, dilemma/decision case, directed case, interrupted case, clicker case, a flipped case, a laboratory case. 
• Different types of teaching methods: problem-based learning, discussion, debate, intimate debate, public hearing, trial, jigsaw, role-play. 

Columbia Resources

Resources available to support your use of case method: The University hosts a number of case collections including: the Case Consortium (a collection of free cases in the fields of journalism, public policy, public health, and other disciplines that include teaching and learning resources; SIPA’s Picker Case Collection (audiovisual case studies on public sector innovation, filmed around the world and involving SIPA student teams in producing the cases); and Columbia Business School CaseWorks , which develops teaching cases and materials for use in Columbia Business School classrooms.

Center for Teaching and Learning

The Center for Teaching and Learning (CTL) offers a variety of programs and services for instructors at Columbia. The CTL can provide customized support as you plan to use the case method approach through implementation. Schedule a one-on-one consultation. 

Office of the Provost

The Hybrid Learning Course Redesign grant program from the Office of the Provost provides support for faculty who are developing innovative and technology-enhanced pedagogy and learning strategies in the classroom. In addition to funding, faculty awardees receive support from CTL staff as they redesign, deliver, and evaluate their hybrid courses.

The Start Small! Mini-Grant provides support to faculty who are interested in experimenting with one new pedagogical strategy or tool. Faculty awardees receive funds and CTL support for a one-semester period.

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• The origins of this method can be traced to Harvard University where in 1870 the Law School began using cases to teach students how to think like lawyers using real court decisions. This was followed by the Business School in 1920 (Garvin, 2003). These professional schools recognized that lecture mode of instruction was insufficient to teach critical professional skills, and that active learning would better prepare learners for their professional lives. ↩
• Golich, V.L. (2000). The ABCs of Case Teaching. International Studies Perspectives. 1, 11-29. ↩
• Herreid, C.F. (2007). Start with a Story: The Case Study Method of Teaching College Science . National Science Teachers Association. Available as an ebook through Columbia Libraries. ↩
• Davis, B.G. (2009). Chapter 24: Case Studies. In Tools for Teaching. Second Edition. Jossey-Bass. ↩
• Andersen, E. and Schiano, B. (2014). Teaching with Cases: A Practical Guide . Harvard Business Press. ↩
• Lundberg, K.O. (Ed.). (2011). Our Digital Future: Boardrooms and Newsrooms. Knight Case Studies Initiative. ↩
• Heath, J. (2015). Teaching & Writing Cases: A Practical Guide. The Case Center, UK. ↩
• Bonney, K. M. (2015). Case Study Teaching Method Improves Student Performance and Perceptions of Learning Gains†. Journal of Microbiology & Biology Education , 16 (1), 21–28. https://doi.org/10.1128/jmbe.v16i1.846 ↩
• Krain, M. (2016). Putting the Learning in Case Learning? The Effects of Case-Based Approaches on Student Knowledge, Attitudes, and Engagement. Journal on Excellence in College Teaching. 27(2), 131-153. ↩
• Thistlethwaite, JE; Davies, D.; Ekeocha, S.; Kidd, J.M.; MacDougall, C.; Matthews, P.; Purkis, J.; Clay D. (2012). The effectiveness of case-based learning in health professional education: A BEME systematic review . Medical Teacher. 2012; 34(6): e421-44. ↩
• Yadav, A.; Lundeberg, M.; DeSchryver, M.; Dirkin, K.; Schiller, N.A.; Maier, K. and Herreid, C.F. (2007). Teaching Science with Case Studies: A National Survey of Faculty Perceptions of the Benefits and Challenges of Using Cases. Journal of College Science Teaching; Sept/Oct 2007; 37(1). ↩
• Popil, I. (2011). Promotion of critical thinking by using case studies as teaching method. Nurse Education Today, 31(2), 204–207. https://doi.org/10.1016/j.nedt.2010.06.002 ↩
• Weimer, M. (2013). Learner-Centered Teaching: Five Key Changes to Practice. Second Edition. Jossey-Bass. ↩
• Herreid, C.F. (2006). “Clicker” Cases: Introducing Case Study Teaching Into Large Classrooms. Journal of College Science Teaching. Oct 2006, 36(2). https://search.proquest.com/docview/200323718?pq-origsite=gscholar ↩

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Case Study Method Definition, Characteristics, Stages & Sources

Introduction case study method of data collection.

The credit of introducing case study method  goes to Frederic Leplay, an English philosopher. Herbert Spencer adopted it and Healey was the first who supported this method and studied Juvenile Delinquency. Later on sociologists, Anthropologists, Ethnologists and other researcher were interested in the study of various cultures by case study method.

Meaning of Case Study

A case study is a comprehensive study of a social unit of society, which may be a person, family group, institution, community or event. A case study focuses attention on a single unit thoroughly. The aim is that to find out the influencing factors of a social unit and the relationship between these factors and a social unit.

Definitions of Case Study Method

• P.V. Young. Case study is a comprehensive study of a social unit, be it a person, a group of persons, an institution, a community or a family.
• Groode and Hatt. it is a method of exploring and analyzing the life of a social unit.
• C.H. Cooley. Case study depends our perception and gives clear insight into life directory.
• Johoda. Case study is a small inclusive and intensive study of an individual in which investigators brings to bear their skills and method.

Keeping the above definitions in view we conclude that case study is a method of studying a social unit and its aspects deeply and thoroughly.

Characteristics of Case Study

Following are the characteristics

• The number of unit to be studied is small.
• It studies a social unit deeply and thoroughly.
• It is qualitative as well as quantitative.
• It covers sufficient wide cycle of time.
• It has continuity in nature.

Stages in a Case Study Method of Data Collection

The techniques and processes of a case study method are given as following.

• Choice of a case or selection of a problem.
• Description of the events.
• Factors influencing study.
• Data processing.
• Data recording.

Sources of Data for Case Study

• Personal documents, viz diaries, memories, autobiographies, letters etc of the researcher.
• Qualification and interest of the researcher.
• Life history of the respondents.
• Motives and objectives of the study.

Related Articles

• http://orcid.org/0000-0003-3777-8492 Robert M Strongin 1 ,
• http://orcid.org/0000-0002-1328-508X Eva Sharma 2 ,
• http://orcid.org/0000-0003-3443-9794 Hanno C Erythropel 3 ,
• http://orcid.org/0000-0002-5403-7234 Nada O F Kassem 4 ,
• Alexandra Noël 5 ,
• http://orcid.org/0000-0001-5828-055X D H Peyton 1 ,
• http://orcid.org/0000-0003-2274-2454 Irfan Rahman 6
• 1 Chemistry , Portland State University , Portland , Oregon , USA
• 2 Westat Inc , Rockville , Maryland , USA
• 3 Chemical and Environmental Engineering , Yale University , New Haven , Connecticut , USA
• 4 CBEACH , San Diego State University Research Foundation , San Diego , California , USA
• 5 Department of Comparative Biomedical Sciences , Louisiana State University , Baton Rouge , Louisiana , USA
• 6 Department of Environmental Medicine , University of Rochester , Rochester , New York , USA
• Correspondence to Dr Robert M Strongin, Chemistry, Portland State University, Portland, Oregon, USA; rmstrongin{at}gmail.com

Studies of Electronic Nicotine Delivery Systems (ENDS) toxicity have largely focused on individual components such as flavour additives, base e-liquid ingredients (propylene glycol, glycerol), device characteristics (eg, model, components, wattage), use behaviour, etc. However, vaping involves inhalation of chemical mixtures and interactions between compounds can occur that can lead to different toxicities than toxicity of the individual components. Methods based on the additive toxicity of individual chemical components to estimate the health risks of complex mixtures can result in the overestimation or underestimation of exposure risks, since interactions between components are under-investigated. In the case of ENDS, the potential of elevated toxicity resulting from chemical reactions and interactions is enhanced due to high operating temperatures and the metallic surface of the heating element. With the recent availability of a wide range of e-liquid constituents and popularity of do-it-yourself creation of e-liquid mixtures, the need to understand chemical and physiological impacts of chemical combinations in ENDS e-liquids and aerosols is immediate. There is a significant current knowledge gap concerning how specific combinations of ENDS chemical ingredients result in synergistic or antagonistic interactions. This commentary aims to review the current understanding of chemical reactions between e-liquid components, interactions between additives, chemical reactions that occur during vaping and aerosol properties and biomolecular interactions, all of which may impact physiological health.

• Electronic nicotine delivery devices
• Non-cigarette tobacco products

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:  http://creativecommons.org/licenses/by-nc/4.0/ .

https://doi.org/10.1136/tc-2023-058546

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What this paper adds

Electronic Nicotine Delivery Systems (ENDS) usage results in exposure to complex chemical mixtures.

ENDS risk assessments for regulatory purposes mainly rely on assessments of individual chemicals or of composite commercial mixtures of e-liquids and/or their corresponding aerosols. There is a significant knowledge gap concerning the health risks from the combined exposure to multiple chemicals from ENDS usage.

This brief report highlights recent studies showing that specific combinations of compounds associated with ENDS can lead to altered chemical emission profiles or non-additive biological effects.

Introduction

The impact of Electronic Nicotine Delivery Systems (ENDS) toxicity on physiological health is an ongoing concern and a better understanding is needed to guide research themes and regulations. The toxicity of ENDS depends on factors including vaping patterns of an individual, device design and operation, power and resulting heat output, as well as the chemical makeup of the refill liquid (‘e-liquid’). 1 Vaping involves aerosolising mixtures of nicotine, solvents, flavorants and various other additives. As of 2017, there were approximately 15 500 available e-liquid formulations 2 comprised of >200 flavorant chemicals. 3 The number of e-liquid formulations appears to have trended upwards to the present time since a 2017 study, which is the most thorough recent report to date. For example, a study published in 2021 reported close to 20 000 different commercial e-liquids with 250 flavour descriptors. 4 Furthermore, do-it-yourself (DIY) e-liquid preparation, wherein people who use ENDS create their own e-liquid mixtures, has become increasingly popular, in part as a reaction to an enforcement policy of flavoured cartridge-based ENDS. 5 6 The popularity of mixing e-liquid flavours in the USA was reported in Wave 2 (2014–2015) of the Population Assessment of Tobacco and Health Study, a nationally representative study of youth (12–17 years) and adults (18+ years), where 38.7% youth and 21.8% adults who used ENDS in the past 30 days reported using more than one flavour in their e-liquid. 7

There has been extensive effort in the ENDS field towards the analysis of commercial e-liquid and aerosol chemical components. Gas chromatography and liquid chromatography, incorporating a variety of detection systems, particularly mass spectrometry, are the major analytical methods used to date. 1 However, a wide variety of specific sampling and analytical techniques have been developed for ENDS research 1 to address the challenging complexity and dynamics of the ENDS product landscape. 8

ENDS risk assessments for regulatory purposes largely rely on assessments of individual chemicals or of composite commercial mixtures of e-liquids and/or their corresponding aerosols. There is a significant knowledge gap concerning the health risks from the combined exposure to multiple chemicals from ENDS usage. For example, chemical studies have shown that ENDS solvents and other molecular components can undergo incomplete combustion (thermal oxidation) reactions to a varying degree, depending on the device power, e-liquid makeup and puffing behaviour. 1 Indeed, e-cigarettes have also been described as ‘chemical reactors’ in literature. 9 10 Other reactions besides incomplete combustion may also occur between specific e-liquid ingredients, such as flavorant acetal formation during storage, thereby further altering molecular structures and properties, which contributes to the complex chemical mixtures of ENDS aerosols. 11 Moreover, studies of the in vitro or in vivo biological effects of vaping have focused on either a specific e-liquid chemical ingredient, such as a single additive, or on exposure to commercial, composite e-liquids or aerosols thereof. 12 However, it is well-known in the pharmaceutical field that different drug molecules may produce non-additive synergistic or antagonistic physiological effects when used in combination. 13

Herein, this paper aims to describe the current understanding of chemical and biological properties of specific chemical combinations found in ENDS e-liquids and aerosols. This issue is relatively under-investigated, 14 15 but is timely and significant considering the extensive availability of e-liquid formulations and the popularity of DIY vaping. The examples described below provide evidence that interactions between certain e-liquid ingredients can lead to unique, non-additive toxicological effects.

Chemical reactions between e-liquid components

A major difference between e-cigarettes and cigarettes is the fact that e-cigarette chemical formulations are liquids: it is well-known that organic molecules are typically more reactive in solution since dissolution enhances intermolecular interactions. For example, a striking illustration of changes to e-liquid compositions on storage was discovered by Erythropel et al . Their findings suggested that common aldehyde flavorants such as benzaldehyde, cinnamaldehyde, citral, ethylvanillin and vanillin readily react with the e-liquid solvents propylene glycol (PG) and glycerol (GL) to form substantial amounts of new compounds (acetals, conversions of 50%–95% depending on the aldehyde), within a timeframe of days to weeks, depending on the aldehyde in question. As expected, the resulting acetals exhibited differential physiological properties from either the flavorant or solvent components that form the respective acetal under the exclusion of a water molecule. PG-derived acetals diminished cellular energy metabolic functions, including basal respiration, ATP production and spare respiratory capacity. 16 PG/GL acetals induced cultured bronchial epithelial cell death at lower concentrations than the parent aldehydes. 17

Interestingly, a study from the Netherlands (NL) did not detect benzaldehyde in a representative sample of 320 NL-marketed e-liquids. 18 However, benzaldehyde was reported by industry in the EU-CEG dataset to be present in 12.4% of >16 k NL-marketed e-liquids 19 It is quite possible that this inconsistency between reported data and analytical measurements is a result of benzaldehyde reactivity, such as with PG or GL to form acetals, or that the sample of commercial e-liquids did not contain benzaldehyde. Kerber et al later demonstrated that acetal formation could be inhibited by nicotine or water, but was promoted by the presence of benzoic acid. 20 Gschwend et al identified additional flavorant adducts, including acetals derived from ketones. They also found acetals in 32% (n=142) of the sampled commercial e-liquids. 21 Overall, it is concerning that several frequently used aldehyde flavorants are transformed to different species through reactions with the e-liquid solvents under storage conditions. This leads to new compounds that also exhibit unique toxicological properties, and occurs in potentially one-third, or more, 20 of all commercial products.

Toxicological interactions between flavorant/additive molecules

Muthumalage et al were the first to determine that mixtures of e-liquid components can exhibit synergistic interactions. 22 They discovered that flavorants trigger reactive oxygen species (ROS) production and an associated inflammatory response in monocytes. Higher production of ROS (and cytotoxicity) was found in a 10 flavorant e-liquid mixture than was anticipated from the sum of the contributions of each specific flavorant. 22 The authors concluded that mixing multiple e-liquid flavorants caused the greatest cytotoxicity, implying a bigger health risk when mixtures of flavorants are present ve a single flavorant.

Marescotti et al found that, of 28 flavorants studied, 2-acetylthiazole, allyl hexanoate, α-pinene, citronellol, guaiacol, linalool, methyl anthranilate, 3-methyl-2,4-nonanedione, 3-(methylthiol) propionaldehyde and phenethyl alcohol each resulted in human bronchial epithelial cell cytotoxicity. 23 24 When mixtures were investigated, cytotoxic properties deviated from the cytotoxicity observed using one specific flavorant. Citronellol had the greatest impact on mixture toxicity, whereas other chemicals resulted in synergistic effects. 23

A study by Baldovinos et al analysed the cytotoxic effects of individual compounds and binary mixtures of a representative terpene ( R -limonene) and an additive (triethyl citrate) on human lung cell models. 25 Data were analysed to determine the effects of 97:3 and 80:20% v/v (triethyl citrate/limonene) binary mixtures on BEAS-2B and A549 cells. LC 50 values and isobolograms were used to assess toxicity and chemical interactions. The data showed that limonene were more cytotoxic than triethyl citrate. Isobolographic analyses confirmed that the mixtures resulted in an antagonistic chemical interaction (ie, reduced toxicity). Further testing of different ratios of binary mixtures is needed for chemical interaction screening to inform safety assessments.

Larcombe et al investigated potential synergistic toxicity between nicotine and e-liquid solvents. 26 Using a mouse model, they showed that inhalation of 0/100% PG/GL aerosols, with or without 12 mg/mL of nicotine, impaired lung function (airway resistance, tissue damping and elastance) in a more pronounced manner than similar ENDS aerosols composed of 100/0% PG/GL. In this study, the presence of nicotine did not significantly impact the altered lung physiological responses, indicating that the inhalation of ENDS aerosols can impair lung function independently of nicotine content. Although an interaction between nicotine and e-liquid solvents leading to impaired lung function was not observed, this study revealed that ENDS solvents alone can induce adverse pulmonary effects in vivo. 26 However, molecular interactions between e-liquid solvents and nicotine impact nicotine exposure. For example, e-liquids composed of >70 % PG have been found to aerosolise faster and lead to greater nicotine aerosol concentrations than GL-rich e-liquids. 27 This was further confirmed in people who used ENDS wherein PG-rich e-liquids was associated with increased nicotine delivery. 28 29

Taken together, these in vitro and in vivo studies show toxicological interactions following exposures to e-liquid constituents, since non-additive toxicological effects of individual e-liquid components were noted. Despite these observations, no mechanisms or chemical reactions/interactions underlying these effects were evaluated. Thus, the chemical interactions between the e-liquid constituents leading to synergetic toxicological effects are still mainly unknown. A recent study by Pappas et al , 30 however, showed that interaction between acids in nicotine salt with coil metals resulted in enhanced transfer of metal oxide, highlighting a mechanism by which e-liquid constituents and ENDS design characteristics interact, and by this mean, may lead to increased toxicity.

Chemical reactions that occur during vaping

Molecular changes can be promoted during vaping due to catalytic reactions on the metal surface of ENDS heating filaments. Saliba et al 31 reported that the metal wires (eg, the iron/chromium/aluminium alloy Kanthal, stainless steel and the nickel/chromium alloy black nichrome) promoted the breakdown of PG to toxic carbonyls such as formaldehyde, methyl glyoxal and acetaldehyde, at temperatures <250°C, and as low as <80°C. 31 Importantly, this is further evident that dry coils and overheating are not the sole reasons 32 for elevated carbonyl toxicant emissions in vaped aerosols.

Formaldehyde derived from partial combustion of PG and GL during vaping has been shown to react with PG and GL to form new formaldehyde derivatives (hemiacetals). 33 Unlike gaseous formaldehyde, which is water soluble and deposits largely in the upper respiratory tract, the hemiacetals are less water soluble and preferentially partition into the aerosol particulate phase. They can thus be delivered more deeply into the airways/lungs than gaseous formaldehyde, which is concerning. 34

The examples described above embody strong evidence that interactions between certain e-liquid ingredients can lead to chemical reactions as well as cause unique, non-additive toxicological effects. Awareness and understanding of the health-related impact of specific combinations of ingredients is thus a necessary and important step to better understand the complex mixtures that e-cigarette liquids and importantly, the aerosols that users are actually exposed to, are. In turn, regulators and researchers should build on the existing although limited knowledge of the toxicity of mixtures as one important tool of many to better understand the toxicity of e-cigarette aerosol mixtures if the goal is to offer safer, truly lower risk alternatives to cigarettes, and to effectively protect public health in light of thousands of existing flavour combinations.

Ethics statements

Patient consent for publication.

Not applicable.

Ethics approval

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X @hanno_ery

Contributors The authors contributed equally to writing and editing this manuscript. RMS, HCE, ES, NOFK, AN, DHP and IR contributed to planning, research, writing and proofreading.

Funding This study is a cross-institution collaborative project from the Toxicity Special Interest Group (SIG) supported, in part, by the Center for Coordination of Analytics, Science, Enhancement and Logistics (CASEL) in Tobacco Regulatory Science U54DA046060 (National Institute of Drug Abuse (NIDA) and the Food and Drug Administration’s Center for Tobacco Products (FDA CTP). Support for authors was also provided by NIDA and FDA CTP awards R01ES025257 (RMS and DHP), U54DA036151 (HCE), U54DA036105, R03ES029441-02S1 (AN), U54 CA228110 (IR), T30IR0894 (NOFK) and U54DA046060-01 (ES). The content of this paper is solely the responsibility of the authors and does not represent the official views of the co-authors’ institutions, the NIH, or the FDA.

Competing interests There are no competing interests.

Provenance and peer review Not commissioned; externally peer reviewed.

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