In which study design is relative risk most appropriately calculated?

• A. Relative risk is most appropriately calculated in cohort studies where incidence can be directly measured.
• B. Relative risk is only used in case-control studies.
• C. Relative risk is best for cross-sectional studies.
• D. Relative risk is not used in public health research.

Answer: (A)

Relative risk compares the chance of developing an outcome between exposed and unexposed groups by using incidence data over time. In a cohort study, people are followed forward in time and new cases are recorded as they occur, so you can directly measure incidence in each group and compute the risk ratio. This direct access to incidence makes relative risk the most appropriate measure in this design.

In case-control studies, you start with people who already have or do not have the outcome and then look back at exposure. Because the study design does not provide incidence data, relative risk cannot be directly calculated; instead, the odds ratio is typically used to summarize association.

Cross-sectional studies capture data at a single moment, giving a snapshot of prevalence rather than incidence. While you can estimate prevalence ratios, a true relative risk requires incidence data collected over time, which these designs do not provide.

Public health research uses multiple measures, and saying relative risk isn’t used at all isn’t accurate. The cohort design remains the best setting for calculating relative risk because it yields direct incidence information.