What defines a case-control study?

A case-control study is characterized by its focus on comparing two distinct groups: individuals who have a specific condition or outcome (the cases) and those who do not have that condition (the controls). This design is particularly useful for understanding the potential causes or risk factors associated with diseases or other health outcomes.

In this study type, researchers look back retrospectively to assess how often exposure to a particular risk factor is present in each group, thereby helping to identify associations between exposures and outcomes. The key features of a case-control study are its observational nature and its ability to efficiently study rare conditions or diseases by focusing on the outcomes of interest first rather than following individuals over time, which is common in prospective studies.

The other options describe different types of study designs. Specifically, a study that manipulates the independent variable refers to an experimental design, longitudinal studies focus on tracking changes over time within the same individuals, and random sampling pertains to the process of selecting individuals from a larger population to ensure representativeness, which is not the primary focus of case-control studies.