Case studies are appropriate for many different situations. This kind of qualitative descriptive research tries to describe the overall situation and attempts to define the variables involved. Quantitative research, on the other hand, attempts to find relationships among variables. Oftentimes, qualitative research will discover what variables need to be further explored in additional qualitative or quantitative research. Case studies are appropriate for situations that are complex or highly contextual.
Case study subjects are often chosen from a group of volunteers. Researchers should attempt to gather subjects with varied backgrounds. These background differences between subjects can be differences in sex, race, experience level, knowledge level, socioeconomic status, etc. Unlike quantitative research, qualitative research does not seek to control any of these variables that may effect outcomes.
In case studies, data is collected in a variety of ways. The researcher's memory, notes, tape recordings, interviews, subjects talking aloud through their thought processes, relevant records and past research can all be used in case studies. All of these methods can bring new information and insights into the research, but each new method carries additional risk of not being seen as valid or reliable.
Case studies don't seek to find "facts" in the same sense that quantitative research does. Instead they "report results in the form of extensive descriptions, conclusions, hypotheses, and questions for further research." Generalizations are limited because researchers do not want to assume that the results of a case study will apply to every case. But when supported by other research, case studies can support certain findings and results.