Which description best defines a cross-sectional study?

• A. It measures exposure and outcome simultaneously at a single point in time
• B. It follows a group over time to assess incidence
• C. It is always prospective
• D. It cannot be used to study associations

Answer: (A)

A cross-sectional study provides a snapshot by measuring both exposure and outcome at the same time in a defined population. This design captures the prevalence of a condition or exposure and can reveal associations between variables present at that moment. It does not follow people over time to observe new cases, which is what a cohort study does to assess incidence. It isn’t inherently prospective; data can be collected at a single time point, even using retrospective information, but the defining feature is the one-time measurement rather than longitudinal follow-up. While you can detect associations in cross-sectional data, temporal order isn’t established, so causality can’t be inferred.