Testing mediators of intervention effects in randomized controlled trials: An evaluation of two eating disorder prevention programs.

The authors investigated mediators hypothesized to account for the effects of 2 eating disorder prevention programs using data from 355 adolescent girls who were randomized to a dissonance or a healthy weight intervention or an active control condition. The dissonance intervention produced significant reductions in outcomes (body dissatisfaction, dieting, negative affect, bulimic symptoms) and the mediator (thin-ideal internalization), change in the mediator correlated with change in outcomes and usually occurred before change in outcomes, and intervention effects became significantly weaker when change in the mediator was partialed, providing support for the hypothesized mediators and this new approach to testing mediation in randomized trials. Findings provide somewhat less support for the hypothesis that change in healthy eating and exercise would mediate the healthy weight intervention effects.