Quantitative Analysis of Factors of Attrition in a Double-blind rTMS Study for Alzheimer Treatment.

Attrition is a particular concern in studies examining the efficacy of a treatment for Alzheimer disease. Analyzing reasons for withdrawal in Alzheimer studies is crucial to ruling out attrition bias, which can undermine a study's validity. In contrast, attrition in studies using repetitive transcranial magnetic stimulation (rTMS) has received much less attention. Our goal was to identify any commonalities between participants who withdrew for the same reasons. Three independent coders rated each response concerning the reasons for withdrawal, and frequency tables were generated to characterize the participants within each category. This study was conducted on the 28 withdrawn cases from a 7-month study investigating the short-term and long-term therapeutic effects of rTMS for Alzheimer disease among 156 participants across 3 sites of the study. Seven reasons for withdrawal were identified, with health and medical changes being the most commonly reported reason (7 participants). Personal issues involving family or caregivers were the next most common (5 participants), and the remaining 5 categories consisted of 3 participants each. Although the limited sample size prevented the use of inferential statistics, our findings highlight the need for more transparent reporting of attrition rates and withdrawal reasons by rTMS researchers.