Increasing psychological flexibility is associated with positive therapy outcomes following a transdiagnostic ACT treatment

Increasing psychological flexibility is considered an important mechanism of change in psychotherapy across diagnoses. In particular, Acceptance and Commitment Therapy (ACT) primarily aims at increasing psychological flexibility in order to live a more fulfilling and meaningful life. The purpose of this study is to examine 1) how psychological flexibility changes during an ACT-based treatment in a transdiagnostic day hospital and 2) how this change is related to changes in symptomatology, quality of life, and general level of functioning.90 patients of a psychiatric day hospital participated in the study. Psychological flexibility, symptomatology, and quality of life were assessed at three measurement time points (admission, discharge, and 3-month follow-up). The level of functioning was assessed at admission and discharge. Differences in psychological flexibility were tested via two-sided paired samples t-tests. Correlations of residualized change scores were calculated to detect associations between changes in psychological flexibility and other outcomes.Psychological flexibility increased significantly from pre-treatment to post-treatment (d = .43, p <.001) and from pre-treatment to follow-up (d = .54, p <.001). This change was significantly correlated to a decrease in symptomatology (r = .60 –.83, p <.001) and an increase in most dimensions of quality of life (r = -.43 – -.75, p <.001) and general level of functioning (r =-.34, p = .003).This study adds further evidence for psychological flexibility as a transdiagnostic process variable of successful psychotherapy. Limitations are discussed.