Past exam of the mathematics course of the University of Cambridge / 2023 / iii / Paper 207 / 5 / ix

The researcher should not selectively add A's post-cutoff death to an analysis explicitly defined by the month-24 data cutoff. Doing so gives extra follow-up to a patient precisely because an event became known, creating outcome-dependent ascertainment. The defensible choices are to retain the locked month-24 analysis or update every patient's record to one common later cutoff and label it as a new analysis.