Abstract

This study elucidates the mechanism of change in the unified protocol for transdiagnostic treatment of emotional disorders (UP). Based on previous findings, we hypothesized that a reduction in psychological inflexibility would act as a mediator of the effects of the UP for anxiety and depression symptoms and impairment in daily functioning, and then examined its mediating effects. Participants were undergraduate students diagnosed with at least one anxiety or depressive disorder according to the DSM-5 criteria. Forty-eight participants in the UP and 17 in the wait-list control condition completed assessments at pre-treatment, post-treatment (8-week interval), and 3-month follow-up. The results of bootstrapping-based mediation analyses indicated that the effects of the UP on the three outcome measures were fully mediated by reductions in psychological inflexibility. In conclusion, the results of this study support the possibility that a reduction in psychological inflexibility may act as a key mechanism of change in the UP.