Case-control studies are preferred in which scenario?

• A. Outbreak investigations.
• B. To measure disease incidence in a population.
• C. Uncommon or long-latency diseases.
• D. When random sampling is easy.

Answer: (C)

Case-control studies are most efficient when the disease is rare or has a long latency from exposure to disease. By starting with individuals who already have the disease (cases) and comparing their past exposures to those without the disease (controls), you can study multiple potential risk factors without waiting to observe enough new cases in a population. This approach requires far fewer subjects and less time than following a large cohort to accumulate incident cases, and it permits assessment of several exposures for a single outcome. Because the outcome is uncommon, the odds ratio from a case-control study closely approximates the relative risk, making it a practical choice for etiologic investigations of rare or long-latency diseases.

Measuring incidence in a population, however, requires following a defined group over time to observe new cases, which a case-control design does not provide. While case-control studies can be used in outbreak settings, they are not the default or most efficient choice for incidence measurement or for situations where random sampling is particularly easy; the main strength lies in studying rare or delayed outcomes efficiently.