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.
Case studies can be produced by following a formal research method. These case studies are likely to appear in formal research venues, 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.:5–6
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.
Another suggestion is that case study should be 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.
Case studies may involve both qualitative and quantitative research methods.
In business research, four common case study approaches are distinguished. First, there is the "no theory first" type of case study design, which is closely connected to Kathleen M. Eisenhardt's methodological work. The second type of research design is about "gaps and holes", following Robert K. Yin's guidelines and making positivist assumptions. A third design deals with a "social construction of reality", represented by the work of Robert E. Stake. Finally, the reason for case study research can also be to identify "anomalies"; a representative scholar of this approach is Michael Burawoy. Each of these four approaches has its areas of application, but it is important to understand their unique ontological and epistomological assumptions. There are substantial methodological differences between these approaches.
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 case 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, as seen in cases selected for more qualitative safety scientific analyses of accidents. A case may be chosen because of the inherent interest of the case or the circumstances surrounding it. Alternatively it may be chosen because of researchers' in-depth local knowledge; where researchers have this local knowledge they are in a position to "soak and poke" as Richard Fenno put 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 for selection:
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 subject and the object of the case study. The subject is the "practical, historical 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. Gary 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.
Some cases study marketing analysis to ensure a full understanding of the effects on an organization. In a case where the market of any organization is in jepoardy, the agency will seek answers and solutions. In order to fulfill this need, the organization must gather pertient information. Case studies can be used to establish where the problem originates by utilizing several research methods.  Research methods should be chosen appropriately to conduct a thorough investigation. The primary methods used include: interviews, surveys, focus groups, observations and in some cases, field trials. The methods chosen rely heavily on the amount of capital the organization is able to spend and the kind of data that is required by the group.
Under the more generalized category of case study exist several subdivisions, each of which is custom selected for use depending upon the goals of the investigator. These types of case study include the following:
Illustrative case studies. These are primarily descriptive studies. They typically utilize one or two instances of an event to show the existing situation. Illustrative case studies serve primarily to make the unfamiliar familiar and to give readers a common language about the topic in question.
Exploratory (or pilot) case studies. These are condensed case studies performed before implementing a large scale investigation. Their basic function is to help identify questions and select types of measurement prior to the main investigation. The primary pitfall of this type of study is that initial findings may seem convincing enough to be released prematurely as conclusions.
Cumulative case studies. These serve to aggregate information from several sites collected at different times. The idea behind these studies is that the collection of past studies will allow for greater generalization without additional cost or time being expended on new, possibly repetitive studies.
Critical instance case studies. These examine one or more sites either for the purpose of examining a situation of unique interest with little to no interest in generalization, or to call into question a highly generalized or universal assertion. This method is useful for answering cause and effect questions.
Research in business disciplines is usually based on a positivistepistemology, namely, that reality is something that is objective and can be discovered and understood by a scientific examination of empirical evidence. But organizational behavior cannot always be easily reduced to simple tests that prove something to be true or false. Reality may be an objective thing, but it is understood and interpreted by people who, in turn, act upon it, and so critical realism, which addresses the connection between the natural and social worlds, is a useful basis for analyzing the environment of and events within an organization.
Case studies in management are generally used to interpret strategies or relationships, to develop sets of "best practices", or to analyze the external influences or the internal interactions of a firm. With several notable exceptions (e.g., Janis on Groupthink)
Frederic Le Play first introduced the case-study method into social science in 1829 as a handmaiden to statistics in his studies of family budgets.
One of the areas in which case studies have been gaining popularity is education and in particular educational evaluation.
Comparative case studies, in social science, policy, and education research; discusses one approach, which encourages researchers to compare horizontally, vertically, and temporally.
Using case studies in research differs from their use in teaching, where they are commonly called case methods and casebook methods. Teaching case studies have been a highly popular pedagogical format in many fields ranging from business education to science education. Harvard Business School has been among the most prominent developers and users of teaching case studies. Business school faculty generally develop case studies with particular learning objectives in mind. Additional relevant documentation, such as financial statements, time-lines, and short biographies, often referred to in the case study as exhibits, and multimedia supplements (such as video-recordings of interviews with the case subject) 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.
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