Which study design measures exposure and disease in a population at a single point in time?

• A. Case-control
• B. Cross-sectional
• C. Cohort
• D. Randomized trial

Answer: (B)

Cross-sectional studies capture exposure and disease status in individuals at a single point in time, like a snapshot of the population. This design is ideal for estimating how common a disease or an exposure is (prevalence) and for identifying associations between exposures and outcomes as they exist at that moment. However, because both exposure and disease are measured together, you can’t tell which came first, so it doesn’t establish temporality or causality.

For context, case-control studies start with people who have the disease and look back to see who was exposed; cohort studies start with exposure status and follow people over time to see who develops the disease; randomized trials assign the exposure to participants to compare outcomes.