I emphasize "consequential" deliberately. When a coordinator misclassifies a participant who has discontinued the study intervention as "withdrawn from the study," the site may stop collecting follow-up data that the protocol requires and the analysis plan depends upon. When a coordinator treats a participant who has withdrawn as merely "discontinued," the site may continue contacting someone who has explicitly asked to be left alone — a violation of their autonomy and potentially of data protection regulations. And when a coordinator treats a participant who has been lost to follow-up as "withdrawn," the site's retention metrics look better on paper but the underlying data quality problem goes unaddressed.

These are not theoretical errors. I have seen every one of them during site audits and monitoring visits. The root cause, in most cases, is that the coordinator was never taught the distinction with sufficient precision — or was taught it once during training and forgot it under the operational pressures of a busy site. This lesson exists to ensure you understand the distinction clearly enough that it becomes automatic.

I emphasize "consequential" deliberately. When a coordinator misclassifies a participant who has discontinued the study intervention as "withdrawn from the study," the site may stop collecting follow-up data that the protocol requires and the analysis plan depends upon. When a coordinator treats a participant who has withdrawn as merely "discontinued," the site may continue contacting someone who has explicitly asked to be left alone — a violation of their autonomy and potentially of data protection regulations. And when a coordinator treats a participant who has been lost to follow-up as "withdrawn," the site's retention metrics look better on paper but the underlying data quality problem goes unaddressed.

These are not theoretical errors. I have seen every one of them during site audits and monitoring visits. The root cause, in most cases, is that the coordinator was never taught the distinction with sufficient precision — or was taught it once during training and forgot it under the operational pressures of a busy site. This lesson exists to ensure you understand the distinction clearly enough that it becomes automatic.