Every protocol specifies a schedule of visits. Visit 1 on Day 1. Visit 2 on Day 15. Visit 3 on Day 29. Visit 8 on Day 169. Each visit has a target date calculated from a reference point — typically the date of randomization or first dose — and each target date comes with a window: the range of days within which that visit may acceptably occur. Day 15 plus or minus three days. Day 29 plus or minus five days. Day 169 plus or minus seven days.

These windows are not suggestions. They are protocol-specified parameters that define when data collection is scientifically valid. A trough drug level drawn on Day 12 instead of Day 15 may be pharmacokinetically meaningless. An efficacy assessment performed on Day 40 instead of Day 29 introduces variability that undermines the statistical analysis. And an out-of-window visit is, by definition, a protocol deviation — one that must be documented, reported, and explained.

I have seen coordinators treat visit scheduling as a clerical task. It is not. It is the operational foundation of protocol compliance, and the coordinators who manage it well are the ones whose sites produce clean data and satisfied participants. The ones who manage it poorly spend their days writing deviation reports and scrambling to reschedule visits that should have been confirmed a week earlier.

Every protocol specifies a schedule of visits. Visit 1 on Day 1. Visit 2 on Day 15. Visit 3 on Day 29. Visit 8 on Day 169. Each visit has a target date calculated from a reference point — typically the date of randomization or first dose — and each target date comes with a window: the range of days within which that visit may acceptably occur. Day 15 plus or minus three days. Day 29 plus or minus five days. Day 169 plus or minus seven days.

These windows are not suggestions. They are protocol-specified parameters that define when data collection is scientifically valid. A trough drug level drawn on Day 12 instead of Day 15 may be pharmacokinetically meaningless. An efficacy assessment performed on Day 40 instead of Day 29 introduces variability that undermines the statistical analysis. And an out-of-window visit is, by definition, a protocol deviation — one that must be documented, reported, and explained.

I have seen coordinators treat visit scheduling as a clerical task. It is not. It is the operational foundation of protocol compliance, and the coordinators who manage it well are the ones whose sites produce clean data and satisfied participants. The ones who manage it poorly spend their days writing deviation reports and scrambling to reschedule visits that should have been confirmed a week earlier.