Which statement best describes data collection in a prospective cohort study?

• A. Data are collected backward in time from disease outcome
• B. Data are collected at a single cross-sectional time
• C. Randomization is used to allocate exposure
• D. Data are collected forward from baseline exposure assessment

Answer: (D)

In a prospective cohort study, data collection moves forward from baseline exposure assessment: you identify a group based on their exposure status, then follow them over time to see who develops the outcome. This forward, time-sequenced approach means exposure is recorded before disease occurs, which helps establish temporality and reduces biases that can come from recalling past exposure. It differs from collecting data backward from an outcome (as in case-control designs), and from a single-time-point cross-sectional snapshot that cannot establish which came first. There is no random assignment of exposure in a cohort study; researchers observe how exposure occurs in the real world and track outcomes as time progresses.