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A case study is a particular method of qualitative research. Rather than using large samples and following a rigid protocol to examine a limited number of variables, case study methods involve an in-depth, longitudinal examination of a single instance or event: a case. They provide a systematic way of looking at events, collecting data, analyzing information, and reporting the results. As a result the researcher may gain a sharpened understanding of why the instance happened as it did, and what might become important to look at more extensively in future research. Case studies lend themselves especially to generating (rather than testing) hypotheses.
The scope and relevance of case studies
Certain disciplines thrive on case studies: others find them less suitable in given situations. Compare usage and perceived validity in the humanities, natural sciences, social sciences, pseudoscience and business.
Rogers, in Business Analysis for Marketing Managers (1978) distinguishes case studies from case histories and projects. He describes a case history as an event or series of events set in an organisational framework with or without a related environment. The events are described in some detail with the main and subsidiary points highlighted. Actions taken by subjects in the case are described; reactions, responses and effects on other subjects are related, and events taken to a conclusion or to a point that is irreversible. Medical cases are typical of the category. Symptoms are described, probable and possible causes suggested, treatment recommended, prognosis recorded, and the date when the patient was discharged or buried.
He defined the case study as also describing events in a framework within an environment. The problems are not always highlighted or even made clear; they emerge as the case material is subjected to analysis. A conclusion is not necessarily stated nor is the situation reached in the case irreversible. It is usually possible to ‘take over’ operations at a suitable point in the role of an external adviser or from a position in the case. Most business cases fall into this category.
The case project is a series of diverse continuous events, set in an organizational framework and normally in a well-defined environment. Those studying the case are led to a specific point in time and circumstance where they become a ‘participant’ in the case. They may be asked to assume the role of a person in the case, appointed to a particular vacancy, or to advise from the position of an external consultant. The role is made explicit and it is from that viewpoint that analysis, views, arguments and recommendations must be made; there is thus a behavioural aspect introduced. If placed in the position of a newly appointed middle manager, responses and suggestions are likely to be different from those of an external consultant. Rogers developed the case project in 1966 for the Chartered Institute of Marketing’s diploma final open book examination. To avoid pre-prepared scripts being submitted, the examination paper progressed the case by several months from when it was published, introducing new material. This required candidates to modify the analyses and conclusions already reached and write a true examination room report.
Types of case study
Illustrative case studies
Illustrative case studies describe a domain; they use one or two instances to analyze a situation. This helps interpret other data, especially when researchers have reason to believe that readers know too little about a program. These case studies serve to make the unfamiliar familiar, and give readers a common language about the topic. The chosen site should typify important variations and contain a small number of cases to sustain readers' interest.
The presentation of illustrative case studies may involve some pitfalls. Such studies require presentation of in-depth information on each illustration; but the researcher may lack time on-site for in-depth examination. The most serious problem involves the selection of instances. The case(s) must adequately represent the situation or program. Where significant diversity exists, no single individual site may cover the field adequately.
Exploratory case studies
Exploratory case studies condense the case study process: researchers may undertake them before implementing a large-scale investigation. Where considerable uncertainty exists about program operations, goals, and results, exploratory case studies help identify questions, select measurement constructs, and develop measures; they also serve to safeguard investment in larger studies.
The greatest pitfall in the exploratory study involves premature conclusions: the findings may seem convincing enough for inappropriate release as conclusions. Other pitfalls include the tendency to extend the exploratory phase, and inadequate representation of diversity.
Critical instance case studies
Critical instance case studies examine one or a few sites for one of two purposes. A very frequent application involves the examination of a situation of unique interest, with little or no interest in generalizability. A second, rarer, application entails calling into question a highly generalized or universal assertion and testing it by examining one instance. This method particularly suits answering cause-and-effect questions about the instance of concern.
Inadequate specification of the evaluation question forms the most serious pitfall in this type of study. Correct application of the critical instance case study crucially involves probing the underlying concerns in a request.
Program implementation case studies
Program implementation case studies help discern whether implementation complies with intent. These case studies may also prove useful when concern exists about implementation problems. Extensive, longitudinal reports of what has happened over time can set a context for interpreting a finding of implementation variability. In either case, researchers aim for generalization and must carefully negotiate the evaluation questions with their customer.
Good program implementation case studies must invest sufficient time to obtain longitudinal data and breadth of information. They typically require multiple sites to answer program implementation questions; this imposes demands on training and supervision needed for quality control. The demands of data management, quality control, validation procedures, and analytic modelling (within site, cross-site, etc.) may lead to cutting too many corners to maintain quality.
Program effects case studies
Program effects case studies can determine the impact of programs and provide inferences about reasons for success or failure. As with program implementation case studies, the evaluation questions usually require generalizability and, for a highly diverse program, it may become difficult to answer the questions adequately and retain a manageable number of sites. But methodological solutions to this problem exist. One approach involves first conducting the case studies in sites chosen for their representativeness, then verifying these findings through examination of administrative data, prior reports, or a survey. Another solution involves using other methods first. After identifying findings of specific interest, researchers may then implement case studies in selected sites to maximize the usefulness of the information.
Prospective case studies
Case studies can be used not only for inductive theory development, but also as quazi-experiments in deductive theory testing. In a prospective case study design, the researcher formulates a set of theory-based hypotheses in respect to the evolution of an on-going social or cultural process and then tests these hypotheses at a pre-determined follow-up time in the future by comparing these hypotheses with the observed process outcomes using "pattern matching" (Campbell, 1966; Trochim, 1989) or a similar technique. This prospective research design consists of (1) a baseline case study, which is used to formulate a set of hypotheses in respect to the evolving social process (i.e., "What predictions would a given theory make in respect to this process?"), establish the follow-up time, follow-up study methodology, and outcome evaluation criteria; and (2) of a follow-up case study conducted at the predetermined follow-up time. In this follow-up study, the formulated hypotheses are compared to the observed outcomes of the social process, and the predictive power of the theory is, thus, evaluated.
Cumulative case studies
Cumulative case studies aggregate information from several sites collected at different times. The cumulative case study can have a retrospective focus, collecting information across studies done in the past, or a prospective outlook, structuring a series of investigations for different times in the future. Retrospective cumulation allows generalization without cost and time of conducting numerous new case studies; prospective cumulation also allows generalization without unmanageably large numbers of cases in process at any one time.
The techniques for ensuring sufficient comparability and quality and for aggregating the information constitute the "cumulative" part of the methodology. Features of the cumulative case study include the case survey method (used as a means of aggregating findings) and backfill techniques. The latter aid in retrospective cumulation as a means of obtaining information from authors that permits use of otherwise insufficiently detailed case studies.
Opinions vary as to the credibility of cumulative case studies for answering program implementation and effects questions. One authority notes that publication biases may favor programs that seem to work, which could lead to a misleading positive view (Berger, 1983). Others raise concerns about problems in verifying the quality of the original data and analyses (Yin, 1989).
Medical case studies
In medical science case studies are considered "Class V" evidence, and are thus the least suggestive of all forms of medical evidence.
History of the case study
As a distinct approach to research, use of the case study originated only in the early 20th century. The Oxford English Dictionary traces the phrase case study or case-study back as far as 1934, after the establishment of the concept of a case history in medicine.
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 as research tools 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. Some of the prominent scholars in educational case study are Robert Stake and Jan Nespor (see references). Case studies have, of course, also been used as a teaching method and as part of professional development. They are well-known in business and legal education. The problem-based learning (PBL) movement is one of the examples. When used in (non-business) education and professional development, case studies are often referred to as critical incidents (see David Tripp in references).
Generalizing from case studies
The case study is 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."
For instance, 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. Galileo’s experimentalism did not involve a large random sample of trials of objects falling from a wide range of randomly selected heights under varying wind conditions, and so on. Rather, it was a matter of a single experiment, that is, a case study.(Flyvbjerg, 2006, p. 225-6) 
Galileo’s view continued to be subjected to doubt, however, and the Aristotelian view was not finally rejected until half a century later, with the invention of the air pump. The air pump made it possible to conduct the ultimate experiment, known by every pupil, whereby a coin or a piece of lead inside a vacuum tube falls with the same speed as a feather. After this experiment, Aristotle’s view could be maintained no longer. What is especially worth noting, however, is that the matter was settled by an individual case due to the clever choice of the extremes of metal and feather. One might call it a critical case, for if Galileo’s thesis held for these materials, it could be expected to be valid for all or a large range of materials. Random and large samples were at no time part of the picture. However it was Galileo's view that was the subject of doubt as it was not reasonable enough to be the Aristotelian view. By selecting cases strategically in this manner one may arrive at case studies that allow generalization.(Flyvbjerg, 2006, p. 225-6) For more on generalizing from case studies, see 
1. Cases selected based on dimensions of a theory (pattern-matching) or on diversity on a dependent phenomenon (explanation-building).
2. No generalization to a population beyond cases similar to those studied.
3. Conclusions should be phrased in terms of model elimination, not model validation. Numerous alternative theories may be consistent with data gathered from a case study.
4. Case study approaches have difficulty in terms of evaluation of low-probability causal paths in a model as any given case selected for study may fail to display such a path, even when it exists in the larger population of potential cases.
The case study offers a method of learning about a complex instance through extensive description and contextual analysis. The product articulates why the instance occurred as it did, and what one might usefully explore in similar situations.
Case studies can generate a great deal of data that may defy straightforward analysis. For details on conducting a case study, especially with regard to data collection and analysis, see the references listed below.
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- 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 
- 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), Oct, 532-550. DOI:10.2307/258557
- Flyvbjerg, Bent. (2006). Five Misunderstandings About Case-Study Research, in Qualitative Inquiry, 12(2): 219-245. Available:
- Bent Flyvbjerg, Making Social Science Matter: Why Social Inquiry Fails and How It Can Succeed Again (Cambridge: Cambridge University Press, 2001). ISBN 052177568X
- George, Alexander L. and Bennett,Andrew. (2005). Case studies and theory development in the social sciences. London, MIT Press 2005. 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.
- Lijphart, Arend.(1971)Comparative Politics and the Comparative Method,in The American Political Science Review, 65(3): 682-693. Available from 
- Ragin, Charles C. and Becker, Howard S. eds. (1992) What is a Case? Exploring the Foundations of Social Inquiry Cambridge: Cambridge University Press. ISBN 0521421888
- Scholz, Roland W. and Tietje, Olaf. (2002) Embedded Case Study Methods. Integrating Quantitative and Qualitative Knowledge. Sage Publications. Thousand Oaks 2002, Sage. ISBN 0761919465 ,9337270973
- Straits, Bruce C. and Singleton, Royce A. (2004) Approaches to Social Research, 4th ed.Oxford University Press. ISBN 0195147944 Available from: 
- The Case Study as a Research Method
- Case Studies
- Darden Business Case Studies
- ETH Zurich: Case studies in Environmental Sciences
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