Which statement best describes end-of-follow-up criteria in a cohort study?

• A. End-of-follow-up is determined solely by administrative end
• B. Death, administrative end, loss to follow-up, and the occurrence of the outcome can end follow-up
• C. End-of-follow-up is determined only by calendar end
• D. End-of-follow-up is determined only by patient withdrawal

Answer: (B)

In a cohort study, end-of-follow-up means the point at which a participant stops contributing observation time. This can happen for several common reasons: the participant dies, they are lost to follow-up, the study ends administratively (the calendar end of the study), or the outcome of interest occurs (which ends observation for that person regarding that outcome). The important idea is that follow-up ends at the earliest time any of these events occur, so the analysis uses the time each person was actually at risk. The other statements are too narrow because they exclude one or more legitimate ways follow-up can end.