The subject of analysis can be a rare or critical event or it can focus on a typical or regular event.
As Seawright and Gerring note, practical considerations such as time and access to information can influence case selection, but these issues should not be the sole factors used in describing the methodological justification for identifying a particular case to study.
Given this, selecting a case includes considering the following: The purpose of a paper in the social sciences designed around a case study is to thoroughly investigate a subject of analysis in order to reveal a new understanding about the research problem and, in so doing, contributing new knowledge to what is already known from previous studies.
A case study paper usually examines a single subject of analysis, but case study papers can also be designed as a comparative investigation that shows relationships between two or among more than two subjects.
The methods used to study a case can rest within a quantitative, qualitative, or mixed-method investigative paradigm.