Life sciences

Case study
In the social and life sciences, a case study is a research method involving an up-close, in-depth, and detailed examination of a particular case. For example, a case study in medicine may examine a specific patient a doctor treated, and a case study in business might study a particular firm's strategy. Generally, a case can be nearly any unit of analysis, including individuals, organizations, events, or actions.
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 in popular works. 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 may involve both qualitative and quantitative research methods.^[1] Single-subject research provides the statistical framework for making inferences from quantitative case-study data.^[2][3] 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. A case study does not necessarily have to be N=1, as there may be many observations within a case (many individuals and entities across many time periods).^[4][5]
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.^{[6][2]:5–6[7]} Case study research have also played a prominent place in business and management research.^[8]

Research methods[edit]
In business research, four common case study approaches are distinguished.^[9][10] First, there is the "no theory first" type of case study design, which is closely connected to Kathleen M. Eisenhardt's methodological work.^[9][11] The second type of research design is about "gaps and holes", following Robert K. Yin's guidelines and making positivist assumptions.^[9][2] A third design deals with a "social construction of reality", represented by the work of Robert E. Stake.^[9][12] Finally, the reason for case study research can also be to identify "anomalies"; a representative scholar of this approach is Michael Burawoy.^[9][13] Each of these four approaches has its areas of application, but it is important to understand their unique ontological and epistemological assumptions. There are substantial methodological differences between these approaches.
Case selection and structure[edit]
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.^[14] 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.^[15][16] 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,^[17] 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:

1. 
   Key cases
   
2. 
   Outlier cases
   
3. 
   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.^[18] 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.^[19]
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.^[20]
John Gerring and Jason Seawright list seven case selection strategies:^[21]

1.