Date of Award




Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Psychology


Clinical Psychology

Content Description

1 online resource (x, 93 pages) : illustrations

Dissertation/Thesis Chair

Mitch Earleywine

Committee Members

Edward Hickling, Drew Anderson


Acceptance and Commitment Therapy, Mechanisms, Mediation, Acceptance and commitment therapy, Self-acceptance, Post-traumatic stress disorder, Mindfulness-based cognitive therapy

Subject Categories



Much of psychotherapy research over the past few decades has focused explicitly on outcomes and neglected examining mediators or mechanisms of change. Not surprisingly, an abundance of outcome research focuses on Acceptance and Commitment Therapy (ACT). Nevertheless, very few studies have examined ACT processes in formal mediation analyses. Three potential mediators of outcomes in ACT include self-compassion, mindfulness, and anxiety sensitivity. The current experiment extends an original evaluation of the effectiveness of two self-help workbooks (traditional Cognitive Behavioral Therapy--CBT--and ACT) for the treatment of anxious suffering in a randomized clinical trial, examining potential simple and multiple mediators responsible for the change in posttraumatic stress disorder- (PTSD) and depression-related symptoms. Participants included an online sample of individuals who self-reported suffering from anxiety. Participants (n = 208) were randomized to one of the two treatment groups and instructed to work through (with no therapeutic guidance) their respective workbooks over the three-month treatment period. Only participants who completed both the pre- and post-treatment assessment batteries (n = 67) were included in the mediation analyses. Each of the three processes (self-compassion, mindfulness, and anxiety sensitivity) singly (simple mediation) mediated the relation between treatment group (CBT or ACT workbook condition) and outcomes (PTSD- and depression-related symptoms). For both PTSD- and depression-related symptoms, the group of mediators as a whole (multiple mediation) mediated the relation between treatment group and outcome. The ACT workbook condition led to better outcomes via the proposed mediators in both the simple and multiple mediation models. In the multiple mediation model of PTSD-related symptoms, anxiety sensitivity emerged as a specific indirect effect, whereas in the multiple mediation model of depression-related symptoms, self-compassion (most important) and anxiety sensitivity (second most important) emerged as specific indirect effects. Self-compassion, mindfulness, and anxiety sensitivity appear to be important mediators of the ACT workbook relative to the CBT workbook. In particular, anxiety sensitivity and self-compassion appear to hold special importance among processes presented in the ACT workbook.

Included in

Psychology Commons