Exposure measurement should include which factors?

• A. Only exposure status
• B. Age and sex
• C. New vs prevalent users; specific drug vs drug class; dose and duration
• D. Follow-up length

Answer: (C)

Measuring exposure accurately means capturing how a person uses a medication over time, not just whether they ever used it. The best approach includes whether the exposure is a new user or a prevalent user, because initiation effects and early exposure periods can carry different risks than established use, and relying on prevalent users can introduce biases and misclassifications of true exposure status. It also distinguishes whether you’re looking at a specific drug or an entire drug class, since different drugs within the same class can have different safety and effectiveness profiles that matter for the association you’re studying. Finally, it records the dose and duration of exposure, enabling assessment of dose–response and cumulative exposure effects that are often critical for understanding risk patterns and for proper exposure categorization.

Exposure status alone misses important nuances like how recently the exposure started, which specific medication was taken, and how much and for how long it was used. Age and sex are important potential confounders to control for, but they aren’t part of how exposure is measured. Follow-up length affects study power and timing of outcomes, but it isn’t a component of exposure measurement itself.