Patient baseline interpersonal problems as moderators of outcome in two psychotherapies for bulimia nervosa

Objective: We tested an aptitude by treatment interaction; namely, whether patients' baseline interpersonal problems moderated the comparative efficacy of cognitive-behavioral therapy (CBT) vs. interpersonal psychotherapy (IPT) for bulimia nervosa (BN). Method: Data derived from a randomized-controlled trial. Patients reported on their interpersonal problems at baseline; purge frequency at baseline, midtreatment, and posttreatment; and global eating disorder severity at baseline and posttreatment. We estimated the rate of change in purge frequency across therapy, and the likelihood of attaining clinically meaningful improvement (recovery) in global eating disorder severity by posttreatment. We then tested the interpersonal problem by treatment interactions as predictors of both outcomes. Results: Patients with more baseline overly communal/friendly problems showed steeper reduction in likelihood of purging when treated with CBT vs. IPT. Patients with more problems of being under communal/cold had similar reductions in likelihood of purging across both treatments. Patients with more baseline problems of being overly agentic were more likely to recover when treated with IPT vs. CBT, whereas patients with more problems of being under agentic were more likely to recover when treated with CBT vs. IPT. Conclusions: Interpersonal problems related to communion and agency may inform treatment fit among two empirically supported therapies for BN.