Internet-based mental health resources often suffer from low engagement and retention. An increased understanding of engagement and attrition is needed to realize the potential of such resources. In this study, 45,142 individuals were screened for depression by an automated online screener, with 2,539 enrolling in a year-long monthly rescreening study; they received a single monthly reminder e-mail to rescreen their mood. We found that, even with such a minimal cohort maintenance strategy, a third of the participants completed 1 or more follow-ups, and 22% completed 2 or more follow-ups. Furthermore, completion of earlier follow-ups was highly predictive of future completions. We also found a number of participant characteristics (e.g., current depression status, previous depression treatment seeking, and education level) predicted follow-up rates, singly or in interactions. 
Participant retention in an automated online monthly depression rescreening program: Patterns and predictors