Which statement about cross-sectional studies is true?

• A. They provide strong evidence of temporality.
• B. They measure exposure and outcome at a single point in time.
• C. They are best for establishing incidence.
• D. They are immune to prevalence-incidence bias.

Answer: (B)

Cross-sectional studies provide a snapshot of exposure and outcome in a population at a single point in time. This design is ideal for estimating how common a disease or exposure is right now and for examining associations between factors as they exist in the moment. However, because data on both exposure and disease are collected simultaneously, you can’t determine which came first, so temporality isn’t established and causality cannot be inferred. They’re not the best for measuring incidence, since they don’t track new cases over time. They’re also susceptible to prevalence‑incidence (Neyman) bias, because conditions with longer durations are more likely to be captured in the study. Therefore, the statement that cross-sectional studies measure exposure and outcome at a single point in time is the accurate description.