Predicting enrollment in two randomized controlled trials of nonpharmacologic interventions for youth with primary mood disorders

Background: As recruitment and retention are often challenging in randomized controlled trials (RCTs), this study sought to identify predictors of participation (i.e., trial enrollment). Method: These analyses identified predictors of enrollment among 119 youth, ages 7–14, with a primary mood disorder, who screened eligible for the Omega-3 and Therapy pilot studies; 95 (79.8%) actually participated in the treatment. Results: Youth who received some form of travel assistance (16.0%) almost uniformly enrolled in the treatment portion of the RCT. Youth who lived further away from the study site (p =.047) or whose primary caregiver never married (p =.01) were less likely to enroll. Of note, socioeconomic status (SES) variables (parent education and child insurance status) did not significantly predict enrollment, suggesting that study incentives or accommodations may have adequately addressed barriers commonly associated with SES. Limitations: Due to the fairly high trial enrollment rate (approximately 80%), there likely was limited power to detect some differences between groups. Generalizability may be limited to youth with a primary mood disorder diagnosis. Conclusions: Despite retaining a large proportion of the youth who screened eligible, participant self-selection is a limitation of any RCT. A silent inclusion criterion of any RCT is willingness to be randomized.