Using the waiting time distribution with random index dates to estimate prescription durations in the presence of seasonal stockpiling

Purpose A pervasive problem in registry‐based pharmacoepidemiological studies is what exposure duration to assign to individual prescriptions. The parametric waiting time distribution (WTD) has been proposed as a method to estimate such durations. However, when prescription durations vary due to seasonal stockpiling, WTD estimates will vary with choice of index date. To counter this, we propose using random index dates. Methods Within a calendar...