Which statement best contrasts cohort studies with case-control studies in toxicology epidemiology?

• A. Case-control studies compare past exposures in individuals with an outcome to those without.
• B. Cohort studies compare exposed and unexposed groups over time to determine outcomes.
• C. Both designs require random assignment to exposure groups.
• D. Case-control studies follow a cohort over time to observe new cases.

Answer: (B)

In toxicology epidemiology, the key difference between cohort and case-control designs is how you start and how you observe outcomes over time. The best statement describes cohort studies as comparing exposed and unexposed groups over time to determine outcomes. Here, you define groups by their exposure status and then follow them forward (prospectively) or look back at records (retrospectively) to see who develops the outcome. This design lets you measure incidence and calculate risk or relative risk.

Context helps: case-control studies, in contrast, begin with the outcome. You identify individuals with the outcome (cases) and without the outcome (controls), then look back to compare past exposures. They’re efficient for studying rare outcomes but don’t provide direct incidence measures. Also, random assignment to exposure is not generally part of these observational designs; randomization is a feature of experimental designs, not typically used in cohort or case-control studies. The idea that case-control studies follow a cohort over time describes a cohort design, not case-control.