There are two ways to learn about a subject. One might study many examples at once, focusing on a few selected dimensions of the phenomena. We shall refer to this as an extensive approach, as laid out in Chapters 7–8.
Alternatively, one might study a particular example, or several examples, in greater depth. We shall refer to this as an intensive, or case study, approach – the topic of this chapter.
A case connotes a spatially delimited phenomenon (a unit) observed at a single point in time or over some period of time. It may be a political unit with a defined area of semi-sovereignty (e.g., empire, nation-state, region, municipality), organization (e.g., firm, non-governmental organization, political party, school), social group (as defined, e.g., by ethnicity, race, age, class, gender, or sexuality), event (e.g., foreign policy crisis, revolution, democratic transition, decision-point), or individual (e.g., a biography, case history).
However defined, a case must comprise the type of phenomenon that an argument attempts to describe or explain. In a study about nation-states cases are comprised of nation-states (observed over time). In a study that attempts to explain the behavior of individuals, cases are comprised of individuals. And so forth.
A case study research design is an intensive study of a single case or a small number of cases that promises to shed light on a larger population of cases. The individual case(s) is viewed as a case of something broader, just as large-sample analysis is also generally viewed as exemplary of a broader phenomenon. Thus, both intensive and extensive analyses generally make inferences from a sample to a population, even though the sample sizes are very different.
Case study research may incorporate one or several cases. The latter is a defining characteristic of comparative historical analysis, associated with the work of Barrington Moore, Theda Skocpol, David Collier, and James Mahoney. However, as the sample of cases expands it becomes less and less feasible to investigate each case intensively. The case study format is thus implicitly a small-sample format.