Research fundamentals: follow-up of subjects in clinical trials: addressing subject attrition.

Many published clinical trials have less than adequate follow-up. When conducting a clinical trial, researchers attempt to minimize data loss; however, some data may not be collected, particularly when subjects are lost to follow-up. Careful planning of research protocols, including comprehensive initial data collection, identification of locators, flexible scheduling, systematic subject tracking, monitoring subject loss, and systematically approaching problem cases can ensure high follow-up rates. This article presents a compendium of techniques and procedures that researchers can use to enhance follow-up and address attrition in their studies. Finally, this article outlines statistical techniques that can be used to address the effects of missing data, particularly when patients are lost to follow-up.