In Chapter Two, I argued that the case study approach to research is most usefully defined as an intensive study of a single unit or a small number of units (the cases), for the purpose of understanding a larger class of similar units (a population of cases). This was put forth as a minimal definition of the topic. In this chapter, I proceed to discuss the nondefinitional attributes of the case study – attributes that are often, but not invariably, associated with the case study method. These will be understood as methodological affinities flowing from our minimal definition of the concept.

The case study research design exhibits characteristic strengths and weaknesses relative to its large-N cross-case cousin. These trade-offs derive, first of all, from basic research goals such as (1) whether the study is oriented toward hypothesis generating or hypothesis testing, (2) whether internal or external validity is prioritized, (3) whether insight into causal mechanisms or causal effects is more valuable, and (4) whether the scope of the causal inference is deep or broad. These trade-offs also hinge on the shape of the empirical universe, that is, on (5) whether the population of cases under study is heterogeneous or homogeneous, (6) whether the causal relationship of interest is strong or weak, (7) whether useful variation on key parameters within that population is rare or common, and (8) whether available data is concentrated or dispersed.