Methods to maximize retention in weight loss studies

Dropouts from clinical trials decrease quality and increase costs. Free participation, paid participation, and contingency contracting are three study retention methods. Contingency contracting, or depositing a fee to be refunded contingent upon attendance in a clinical trial, has been reported to decrease dropouts without affecting weight loss. These three methods of retention were compared with a commercial weight loss clinic's practice of charging nonrefundable fees.

Dropouts were compared in two studies testing mazindol, with one study using free care and the other using contingency contracting; two studies testing phenylpropanolamine, one using free care and the other using contingency contracting; and in studies with phenylpropanolamine on file with Thompson Medical Company using free care, paid participation, and contingency contracting.

The dropout rate was 50% at 8 weeks in a trial of mazindol with free care vs. 7% for contingency contracting (p<0.001). The two phenylpropanolamine studies gave the same weight losses, but the dropouts were 37% at 8 weeks for free care vs. 11% for contingency contracting (p<0.001). The studies of phenylpropanolamine on file at the Thompson Medical Company had 28% dropouts at 8 weeks using free care vs. 19% for paid participation (p<0.001), and 11% for contingency contracting (p<0.005). Dropouts with contingency contracting (11%) were not different from the commercial weight loss program (13%).

Contingency contracting can decrease dropouts, improve quality, and decrease costs without affecting weight loss in clinical trials for obesity.