Advances and controversies in the design of obesity prevention trials.

Because randomized controlled trial designs are used more frequently to evaluate obesity prevention programs, nuances in the methodology used for this application become apparent. Areas of attention are the selection of outcome measures with high validity, attention to the description of the intervention, the use of analyses that match the sampling design, and dealing with loss to follow-up. We recommend increased use of preliminary or evidentiary research designed to develop and test intervention components and hypothesized mediators before fully powered, randomized, obesity prevention trials are attempted. Both randomized and observational designs can be used for the purpose. Attention to design issues will ultimately lead to more successful, cost-effective randomized trials, and more rapid movement toward efficacious and effective obesity prevention programs.