A case-control study is a study in which subjects are selected based on their outcome status, such as with disease or disease-free. Investigators select cases (subjects with the outcome of interest) and controls (subjects without the outcome of interest) and then compare the exposure (or risk factor) status in the two groups.
Case-control studies are a very common observational study design within behavioral medicine research. Because the participants are selected based on their outcome status (commonly disease status), this study design is well suited for an outcome that is rare. For diseases with long latency periods (for example, melanoma or coronary heart disease), case-control studies can also be time efficient because the outcome has already occurred at the initiation of the study. When the exposure (or risk factor) is rare, a case-control study is often not practical.