In the social sciences and life sciences, a case study is a research method involving an up-close, in-depth, and detailed examination of a subject of study (the case), as well as its related contextual conditions. Although no single definition of the case study exists, case-study research has long had a prominent place in many disciplines and professions, ranging from psychology, anthropology, sociology, and political science to education, clinical science, social work, and administrative science.
The "case" being studied may be an individual, organization, event, or action, existing in a specific time and place. For instance, clinical science has produced both well-known case studies of individuals and also case studies of clinical practices. However, when case is used in an abstract sense, as in a claim, proposition, or argument, such a case can be the subject of many research methods, not just a case study.
Thomas offers the following definition of case study:
"Case studies are analyses of persons, events, decisions, periods, projects, policies, institutions, or other systems that are studied holistically by one or more method. The case that is the subject of the inquiry will be an instance of a class of phenomena that provides an analytical frame — an object — within which the study is conducted and which the case illuminates and explicates."
According to J. Creswell, data collection in a case study occurs over a "sustained period of time."
One approach sees the case study defined as a research strategy, an empirical inquiry that investigates a phenomenon within its real-life context. Case-study research can mean single and multiple case studies, can include quantitative evidence, relies on multiple sources of evidence, and benefits from the prior development of theoretical propositions. Case studies should not be confused with qualitative research and they can be based on any mix of quantitative and qualitative evidence. Single-subject research provides the statistical framework for making inferences from quantitative case-study data. This is also supported and well-formulated in (Lamnek, 2005): "The case study is a research approach, situated between concrete data taking techniques and methodologic paradigms."
Case selection and structure
An average, or typical case, is often not the richest in information. In clarifying lines of history and causation it is more useful to select subjects that offer an interesting, unusual or particularly revealing set of circumstances. A case selection that is based on representativeness will seldom be able to produce these kinds of insights. When selecting a subject for a case study, researchers will therefore use information-oriented sampling, as opposed to random sampling. Outlier cases (that is, those which are extreme, deviant or atypical) reveal more information than the potentially representative case. Alternatively, a case may be selected as a key case, chosen because of the inherent interest of the case or the circumstances surrounding it. Alternatively it may be chosen because of a researchers' in-depth local knowledge; where researchers have this local knowledge they are in a position to “soak and poke” as Fenno puts it, and thereby to offer reasoned lines of explanation based on this rich knowledge of setting and circumstances.
Three types of cases may thus be distinguished:
- Key cases
- Outlier cases
- Local knowledge cases
Whatever the frame of reference for the choice of the subject of the case study (key, outlier, local knowledge), there is a distinction to be made between the subjestorical unity  through which the theoretical focus of the study is being viewed. The object is that theoretical focus – the analytical frame. Thus, for example, if a researcher were interested in US resistance to communist expansion as a theoretical focus, then the Korean War might be taken to be the subject, the lens, the case study through which the theoretical focus, the object, could be viewed and explicated.
Beyond decisions about case selection and the subject and object of the study, decisions need to be made about purpose, approach and process in the case study. Thomas thus proposes a typology for the case study wherein purposes are first identified (evaluative or exploratory), then approaches are delineated (theory-testing, theory-building or illustrative), then processes are decided upon, with a principal choice being between whether the study is to be single or multiple, and choices also about whether the study is to be retrospective, snapshot or diachronic, and whether it is nested, parallel or sequential. It is thus possible to take many routes through this typology, with, for example, an exploratory, theory-building, multiple, nested study, or an evaluative, theory-testing, single, retrospective study. The typology thus offers many permutations for case study structure.
A closely related study in medicine is the case report, which identifies a specific case as treated and/or examined by the authors as presented in a novel form. These are, to a differentiable degree, similar to the case study in that many contain reviews of the relevant literature of the topic discussed in the thorough examination of an array of cases published to fit the criterion of the report being presented. These case reports can be thought of as brief case studies with a principal discussion of the new, presented case at hand that presents a novel interest.
Generalizing from case studies
A critical case is defined as having strategic importance in relation to the general problem. A critical case allows the following type of generalization, ‘If it is valid for this case, it is valid for all (or many) cases.’ In its negative form, the generalization would be, ‘If it is not valid for this case, then it is not valid for any (or valid for only few) cases.’
The case study is also effective for generalizing using the type of test that Karl Popper called falsification, which forms part of critical reflexivity. Falsification is one of the most rigorous tests to which a scientific proposition can be subjected: if just one observation does not fit with the proposition it is considered not valid generally and must therefore be either revised or rejected. Popper himself used the now famous example of, "All swans are white," and proposed that just one observation of a single black swan would falsify this proposition and in this way have general significance and stimulate further investigations and theory-building. The case study is well suited for identifying "black swans" because of its in-depth approach: what appears to be "white" often turns out on closer examination to be "black."
Galileo Galilei’s rejection of Aristotle’s law of gravity was based on a case study selected by information-oriented sampling and not random sampling. The rejection consisted primarily of a conceptual experiment and later on of a practical one. These experiments, with the benefit of hindsight, are self-evident. Nevertheless, Aristotle’s incorrect view of gravity dominated scientific inquiry for nearly two thousand years before it was falsified. In his experimental thinking, Galileo reasoned as follows: if two objects with the same weight are released from the same height at the same time, they will hit the ground simultaneously, having fallen at the same speed. If the two objects are then stuck together into one, this object will have double the weight and will according to the Aristotelian view therefore fall faster than the two individual objects. This conclusion seemed contradictory to Galileo. The only way to avoid the contradiction was to eliminate weight as a determinant factor for acceleration in free fall.
History of the case study
It is generally believed that the case-study method was first introduced into social science by Frederic Le Play in 1829 as a handmaiden to statistics in his studies of family budgets. (Les Ouvriers Europeens (2nd edition, 1879).
The use of case studies for the creation of new theory in social sciences has been further developed by the sociologists Barney Glaser and Anselm Strauss who presented their research method, Grounded theory, in 1967.
The popularity of case studies in testing hypotheses has developed only in recent decades. One of the areas in which case studies have been gaining popularity is education and in particular educational evaluation.(MacDonald, B., & Walker, R. (1975) “Case Study and the social philosophy of educational research”. Cambridge Journal of Education 5, pp. 2–11.) (MacDonald, B. (1978) The Experience of Innovation, CARE Occasional Publications #6, CARE, University of East Anglia, Norwich, UK) ( Kushner, S. (2000) Personalizing Evaluation. Thousand Oaks: Sage Publications)
Case studies have also been used as a teaching method and as part of professional development, especially in business and legal education. The problem-based learning (PBL) movement is such an example. When used in (non-business) education and professional development, case studies are often referred to as critical incidents.
Ethnography is an example of a type of case study, commonly found in communication case studies. Ethnography is the description, interpretation, and analysis of a culture or social group, through field research in the natural environment of the group being studied. The main method of ethnographic research is through observation where the researcher observes the participants over an extended period of time within the participants own environment.
As a final observation, using case studies to do research differs from their use in teaching. As stated in Wikipedia's preamble to this article, the article is "about the method of doing research." For the teaching method, the preamble refers readers to separate articles on the Case method and Casebook method. At the same time, many people's first exposure to case studies occurred in the classroom, and teaching case studies have been a highly popular pedagogical format in many fields — ranging from business education to science education.
The Harvard Business School has possibly been the most prominent developer and user of teaching case studies. Business school faculty generally develop case studies with particular learning objectives in mind, and the classroom experiences may lead to refinement prior to publication. Additional relevant documentation (such as financial statements, time-lines, and short biographies, often referred to in the case study as "exhibits"), multimedia supplements (such as video-recordings of interviews with the case protagonist), and a carefully crafted teaching note often accompany the case studies. Similarly, teaching case studies have become increasingly popular in science education. The National Center for Case Studies in Teaching Science  has made a growing body of case studies available for classroom use, for university as well as secondary school coursework.
Nevertheless, the principles in doing case study research contrast strongly with those in doing case studies for teaching. The teaching case studies need not adhere strictly to the use of evidence, as they can be manipulated to satisfy pedagogical needs. The generalizations from teaching case studies also may relate to pedagogical issues rather than the substance of the case being studied. Unfortunately, the contrast between the two types of case studies have not always been appreciated. For this reason, many people have had poor impressions of the validity and generalizability of case study research. The present article will hopefully help to rectify these impressions.
- Casebook method
- Case method
- Case study in psychology
- Case competition
- Case report
- Washington County Closed-Circuit Educational Television Project
- Mills, Albert J.; Gabrielle Durepos; Elden Wiebe. (Eds.). (2010). Encyclopedia of Case Study Research. Sage Publications. California. p. xxxi. ISBN 978-1-4129-5670-3.
- Robert K. Yin. Case Study Research: Design and Methods. 5th Edition. Sage Publications. California, 2014. Pages 5-6. ISBN 978-1-4522-4256-9
- Rolls, Geoffrey (2005). Classic Case Studies in Psychology. Hodder Education, Abingdon, England.
- Suzanne Corkin. Permanent Present Tense: The Unforgettable Life of the Amnesic Patient, H.M.. Basic Books. New York. 2013. ISBN 978-0-4650-3159-7
- Rodger Kessler & Dale Stafford. Editors. Collaborative Medicine Case Studies: Evidence in Practice. Springer. New York. 2008. [ISBN 978-0-3877-6893-9]
- Thomas, G. (2011). "sonia is typing..... A typology for the case study in social science following a review of definition, discourse and structure". Qualitative Inquiry 17 (6): 511–521. doi:10.1177/1077800411409884.
- Creswell, John (2009). Research Design; Qualitative and Quantitative and Mixed Methods Approaches. London: Sage. ISBN 978-1-4522-2609-5.
- Siegfried Lamnek. Qualitative Sozialforschung. Lehrbuch. 4. Auflage. Beltz Verlag. Weihnhein, Basel, 2005
- Fenno, R. (1986). "Observation, context, and sequence in the study of politics". American Political Science Review 80 (1): 3–15. doi:10.2307/1957081.
- M. Wieviorka (1992) Case studies: history or sociology? In C.C. Ragin and H.S. Becker (Eds) What is a case? Exploring the foundations of social inquiry. New York: Cambridge University Press.
- Gary Thomas, How to do your Case Study (Thousand Oaks: Sage, 2011)
- Flyvbjerg, B. (2006). "Five Misunderstandings about Case-Study Research". Qualitative Inquiry 12 (2): 219–245. doi:10.1177/1077800405284363.
- Sister Mary Edward Healy, C. S. J. (1947). "Le Play's Contribution to Sociology: His Method". The American Catholic Sociological Review 8 (2): 97–110. doi:10.2307/3707549.
- Robert E. Stake, The Art of Case Study Research (Thousand Oaks: Sage, 1995). ISBN 0-8039-5767-X
- Encyclopedia of Consumer Culture
- D.A. Garvin (Sept.-Oct.2003) Making the Case: Professional Education for the World of Practice. Harvard Magazine, 106, 1, 56-107
- W. Ellet. The Case Study Handbook: How to Read, Write, and Discuss Persuasively about Cases. Harvard Business School Press. Boston, MA. 2007. [ISBN 978-1-422-10158-2]
- Baxter, P and Jack, S. (2008) "Qualitative Case Study Methodology: Study design and implementation for novice researchers", in The Qualitative Report, 13(4): 544-559. Available from 
- Dubois, Anna; Gadde, Lars-Erik (2000). "Supply strategy and network effects—purchasing behaviour in the construction industry" (PDF). European Journal of Purchasing & Supply Management 6 (3): 207–215. doi:10.1016/s0969-7012(00)00016-2.
- Dul, J. and Hak, T. (2008) Case Study Methodology in Business Research. Oxford: Butterworth-Heinemann. ISBN 978-0-7506-8196-4.
- Eisenhardt, K. M. (1989). "Building theories from case study research". The Academy of Management Review 14 (4): 532–550. doi:10.2307/258557.
- George, Alexander L. and Bennett, Andrew. (2005) Case studies and theory development in the social sciences. London: MIT Press. ISBN 0-262-57222-2
- Gerring, John. (2005) Case Study Research. New York: Cambridge University Press. ISBN 978-0-521-67656-4
- Hancké, Bob. (2009) Intelligent Research Design. A guide for beginning researchers in the social sciences. Oxford University Press.
- Kay, L.; Youtie, J.; Shapira, P. (2014). "Signs of things to come? What patent submissions by small and medium-sized enterprises say about corporate strategies in emerging technologies". Technological Forecasting & Social Change: 17. doi:10.1016/j.techfore.2013.09.006.
- Kyburz-Graber, Regula (2004). "Does case-study methodology lack rigour? The need for quality criteria for sound case-study research, as illustrated by a recent case in secondary and higher education". Environmental Education Research 10 (1): 53–65. doi:10.1080/1350462032000173706.
- Lijphart, Arend. (1971) "Comparative Politics and the Comparative Method", in The American Political Science Review, 65(3): 682-693. Available from 
- Mills, Albert J., Durepos, Gabrielle, and Wiebe, Elden. Eds. (2010) Encyclopedia of Case Study Research. (2 vols.). Thousand Oaks, CA: Sage. ISBN 978-1-4129-5670-3
- Ragin, Charles C. and Becker, Howard S. Eds. (1992) What is a Case? Exploring the Foundations of Social Inquiry. Cambridge: Cambridge University Press. ISBN 0-521-42188-8
- Scholz, Roland W. and Tietje, Olaf. (2002) Embedded Case Study Methods. Integrating Quantitative and Qualitative Knowledge. Thousand Oaks, CA: Sage. ISBN 0-7619-1946-5
- Straits, Bruce C. and Singleton, Royce A. (2004) Approaches to Social Research, 4th ed. Oxford: Oxford University Press. ISBN 0-19-514794-4. Available from: 
- Thomas, Gary. (2011) How to do your Case Study: A Guide for Students and Researchers. Thousand Oaks, CA: Sage.
- Yin, Robert. (2014) Case Study Research: Design and Methods. (5th Edition). Thousand Oaks, CA: Sage.