What is the primary study design of epidemiology?

• A. Randomized controlled trials.
• B. Observational.
• C. Case series.
• D. Experimental.

Answer: (B)

Epidemiology primarily studies health patterns in populations by observing exposures and outcomes without intervening or assigning treatments. This makes observational study designs—the cohort, case-control, and cross-sectional studies—the main tools for investigating associations in real-world settings. Randomized controlled trials and other experimental designs are crucial for testing causality, but they involve active assignment of exposure or intervention and are used when feasible and ethical; they sit alongside epidemiology but are not the standard approach for a broad epidemiologic study design. A case series, being descriptive and without a comparison group, doesn’t provide the analytic framework needed to study determinants of disease. Therefore, observational studies are the most representative answer.