Longitudinal treatment mediation of traditional cognitive behavioral therapy and acceptance and commitment therapy for anxiety disorders.
OBJECTIVE
To assess the relationship between session-by-session putative mediators and treatment outcomes in traditional cognitive behavioral therapy (CBT) and acceptance and commitment therapy (ACT) for mixed anxiety disorders.


METHOD
Session-by-session changes in anxiety sensitivity and cognitive defusion were assessed in 67 adult outpatients randomized to CBT (n = 35) or ACT (n = 32) for a DSM-IV anxiety disorder.


RESULTS
Multilevel mediation analyses revealed significant changes in the proposed mediators during both treatments (p < .001, d = .90-1.93), with ACT showing borderline greater improvements than CBT in cognitive defusion (p = .05, d = .82). Anxiety sensitivity and cognitive defusion both significantly mediated post-treatment worry; cognitive defusion more strongly predicted worry reductions in CBT than in ACT. In addition, cognitive defusion significantly mediated quality of life, behavioral avoidance, and (secondary) depression outcomes across both CBT and ACT (p < .05, R(2) change = .06-.13), whereas anxiety sensitivity did not significantly mediate other outcomes.


CONCLUSIONS
Cognitive defusion represents an important source of therapeutic change across both CBT and ACT. The data offered little evidence for substantially distinct treatment-related mediation pathways.