What is a case-control study design and when is it most appropriate?

• A. Compares exposures between cases and controls to estimate association; good for rare diseases or when outcomes are long-latent.
• B. Follows a cohort over time to observe disease.
• C. Randomized trial.
• D. Descriptive cross-sectional.

Answer: (B)

A case-control study begins with people who have the disease (cases) and people without the disease (controls) and compares their prior exposures to identify associations with the disease. This design is most appropriate when the disease is rare or has a long latency between exposure and outcome, because you can study a small number of cases and examine many potential exposures without waiting for new cases to develop. It yields an odds ratio as a measure of association, which, when the disease is rare, closely estimates the relative risk. The approach is efficient, generally quicker and cheaper than following a cohort over time, but it depends on accurate recall of past exposures and careful selection of controls to minimize bias, and it cannot directly provide incidence or risk over time. In contrast, following a cohort over time to observe disease describes a cohort study, while a randomized trial assigns exposures, and a descriptive cross-sectional study assesses exposure and disease status at a single point in time.