Gap-time recurrent-event model ($g=t-t_{k-1}$)

A gap-time model uses time since the previous recurrence as the episode clock, instead of calendar time since treatment or study entry. Subtract the previous event time from both interval endpoints. Eligibility restrictions become delayed gap entry, and patient/episode labels preserve the actual order of recurrent events. Risk sets on this clock compare eligible episodes of a common gap age, not patients at one common calendar time.