A case study involves an up-close, in-depth, and detailed examination of a subject (the case), as well as its related contextual conditions. Case studies appear with great frequency throughout popular works, with nearly anybody able to claim to have done one. Case studies also can be produced by following a formal research method. These case studies are likely to appear in formal research venues, such as journals and professional conferences, rather than popular works. The resulting body of '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.
In doing case study research, 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, a proposition, or an argument, such a case can be the subject of many research methods, not just case study research.
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. As such, case study research should not be confused with qualitative research, as case studies can be based on any mix of quantitative and qualitative data. Similarly,single-subject research might be taken as case studies of a sort, except that the repeated trials in single-subject research permit the use of experimental designs that would not be possible in typical case studies. At the same time, the repeated trials can provide a statistical framework for making inferences from quantitative data.
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
Other roots stem from the early 20th century, when case studies began taking place in the disciplines of sociology, psychology, and anthropology. In all these disciplines, case studies were an occasion for creating new theory, as in the Grounded Theory work of sociologists Barney Glaser and Anselm Strauss.
The popularity of case studies in testing theory or 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.
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
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