Exploring Moderators and Mediators of the Outcome of Group Cognitive Behavioural Therapy Compared With Group Schema Therapy for Social Anxiety Disorder and Comorbid Avoidant Personality Disorder.

Background: Identifying moderators and mediators in a randomised controlled trial is important to improve treatment effectiveness and elucidate mechanisms of change. Putative moderating and mediating variables of treatment outcome of 30 weekly sessions of group cognitive behavioural therapy (GCBT) and group schema therapy (GST) were investigated in a sample of 154 patients with both social anxiety disorder (SAD) and avoidant personality disorder (AVPD). Significant improvements were realised in both modalities at 3 and 12 months after treatment. No significant differences between conditions were found.

Objectives: The current study explored several demographic and clinical patient characteristics as putative moderators of reducing SAD symptoms, AVPD manifestations, and treatment attrition. Emotion regulation, self-esteem, experiential avoidance and schema modes were considered as putative mediators of SAD symptoms.

Methods: Baseline variables moderating treatment effects on SAD symptoms and AVPD manifestations were investigated by comparing multilevel models. Differential effects of moderators on attrition hazard were examined by Cox regression. To assess possible mediators (measured pre-, mid- and post-treatment) of the effect of GCBT versus GST on SAD symptoms, separate three-wave random-intercept cross-lagged panel models were performed.

Results: No moderators and mediators were identified. Self-esteem, the average mode score and avoidant protector mode at mid-treatment predicted social anxiety at the end of treatment irrespective of treatment condition, while an inverse relationship was ruled out.

Conclusions: The moderator analyses indicated that the examined patient characteristics cannot inform treatment decisions for either GCBT or GST. Furthermore, the mediation analysis did not point to different underlying treatment processes between both modalities.