Acceptance and commitment therapy (ACT) process and outcome: a systematic evaluation of ACT for treatment resistant patients

Although traditional Cognitive Behaviour Therapy (CBT) has achieved many clinical successes, approximately 30-50% of patients are resistant to this form of treatment. This trans-diagnostic group of treatment resistant patients typically have chronic, co-morbid, and/or personality disordered symptoms and often engage in a range of maladaptive behaviours (e.g., substance abuse, deliberate self-harm). Acceptance and Commitment Therapy (ACT) is a relatively modern psychological treatment which proposes that the formally dissimilar symptoms this group present result from a common cause; namely, excessive entanglement with, and a need to escape from or avoid, unwanted private events such as thoughts, feelings, and memories (experiential avoidance). Preliminary evidence from clinical trials suggest that ACT may prove efficacious with treatment resistant patients. In this thesis, four studies were designed to examine the theoretical underpinnings and clinical utility of ACT. Studies 1 and 2 tested the ACT-derived prediction that diverse maladaptive behaviours serve a common experiential avoidance function. In support of this hypothesis, structural equation modelling showed that experiential avoidance predicted significant maladaptive behaviour covariance. Moreover, using the same method, a cross-sectional design showed that experiential avoidance partially mediated the effect of Negative Affect Intensity and Childhood Trauma on the tendency to engage in maladaptive behaviours. Studies 3 and 4 extended these theoretically-based investigations into the applied domain, pilot testing ACT for a sample of patients whose symptoms had been resistant to, or relapsed following, standard care. Study 3, a pre-post uncontrolled trial, revealed significant reductions in psychological distress with gains maintained at 6 and 12-month follow-up. Study 4, a randomised control trial comparing ACT to a CBT treatment as usual (CBT-TAU) condition, showed that ACT achieved more enduring effects than CBT-TAU. Furthermore, exploratory analyses suggested that, for the ACT group alone, reductions in experiential avoidance during treatment predicted follow-up outcomes. These findings support the use of ACT for treatment resistant patients