Which option correctly describes the essential feature of selecting participants in a case-control study?

Which option correctly describes the essential feature of selecting participants in a case-control study?

• A. Selection based on disease status (cases and controls)
• B. Randomization of participants to exposure groups
• C. Prospective recruitment of all participants without disease
• D. Follow-up to observe disease incidence

Answer: (A)

In a case-control study, you form groups by outcome: those with the disease (cases) and those without the disease (controls). The essential feature is selecting participants based on disease status, then looking back to compare their prior exposures. This setup lets you estimate the association between an exposure and the disease, usually using an odds ratio. Why the other approaches don’t fit: randomizing participants to exposure groups is what happens in experimental or randomized trials, not in case-control studies. Prospectively recruiting everyone without disease and following them forward describes a cohort design that tracks who develops disease over time, rather than starting with disease status. Following people to observe disease incidence is also a hallmark of cohort studies, not case-control.

In a case-control study, you form groups by outcome: those with the disease (cases) and those without the disease (controls). The essential feature is selecting participants based on disease status, then looking back to compare their prior exposures. This setup lets you estimate the association between an exposure and the disease, usually using an odds ratio.

Why the other approaches don’t fit: randomizing participants to exposure groups is what happens in experimental or randomized trials, not in case-control studies. Prospectively recruiting everyone without disease and following them forward describes a cohort design that tracks who develops disease over time, rather than starting with disease status. Following people to observe disease incidence is also a hallmark of cohort studies, not case-control.