title: Methods to maximize retention in weight loss studies.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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%).
  
  
  CONCLUSIONS
  Contingency contracting can decrease dropouts, improve quality, and decrease costs without affecting weight loss in clinical trials for obesity.
authors.affiliation: Pennington Biomedical Research Center, Baton Rouge, LA 70808-4124, USA. greenwfl@mhs.pbrc.edu
authors.forename: F L
authors.initials: FL
authors.lastname: Greenway
authors.forename: G A
authors.initials: GA
authors.lastname: Bray
authors.forename: R L
authors.initials: RL
authors.lastname: Marlin
mesh_terms: D001067:Appetite Depressants / Q000627:therapeutic use*; D004311:Double-Blind Method; D006801:Humans; D008454:Mazindol / Q000627:therapeutic use; D010352:Patient Dropouts; D018579:Patient Selection; D010665:Phenylpropanolamine / Q000627:therapeutic use; D010919:Placebos; D015431:Weight Loss
chemical_list: D001067:Appetite Depressants; D010919:Placebos; D010665:Phenylpropanolamine; D008454:Mazindol