Which study design is best to determine prevalence in a population at a single point in time?

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

Answer: (B)

To determine prevalence at a single point in time, you need a study design that provides a snapshot of how common a condition is in the population right now. A cross-sectional study does exactly that: it collects data on exposure and disease status from a sample at one point in time, allowing you to calculate the point prevalence (existing cases divided by the total population surveyed). It’s efficient for measuring how widespread a condition is at that moment without following people over time.

Why the others aren’t as suitable: a case-control study starts with people based on disease status and looks back for exposures, which can bias how common the condition appears in the general population and isn’t aimed at estimating prevalence. A cohort study follows people over time to observe new cases, yielding incidence data and risk factors rather than a one-time prevalence snapshot. A clinical trial involves assigning an intervention and comparing outcomes under controlled conditions, which isn’t designed to estimate how common a condition is in the broader population.