What can cross-sectional studies measure and what is a key limitation?

• A. Incidence over time.
• B. Prevalence measurement with temporality established.
• C. Longitudinal risk assessment.
• D. Prevalence; temporality cannot be established.

Answer: (D)

Cross-sectional studies provide a snapshot of how common a condition is in a population at a single point in time, so they measure prevalence. The key limitation is that they cannot establish temporality—the order of exposure and disease cannot be determined from the data gathered at one moment, so you can’t infer causality or determine whether exposure preceded the outcome. This is why the appropriate description is that prevalence cannot have temporality established. The other statements would require observing new cases over time or following people longitudinally, which cross-sectional designs do not do.