Acceptance and commitment therapy as a transdiagnostic, process-based approach to treatment for mental health concerns: A mechanism of change analysis using a multiple baseline design across participants

Abstract

Although much research exists concerning outcomes of evidence-based psychosocial interventions, relatively less is known about the processes, or mechanisms, of change underlying these interventions. One evidence-based intervention that is commensurate with a process-based, transdiagnostic approach to treatment development is acceptance and commitment therapy (ACT). ACT targets the functionally and contextually defined, systematically manipulable behavioral processes of change that underlie topographically diverse symptomology, and it does so to promote a client’s adaptive behavioral functioning in important life domains. Key exemplars of such processes are engaged living (EL) and experiential avoidance (EA). Using a multiple baseline design across participants, the current study investigated the effects of individually delivered ACT in adults with varied mental health concerns, while simultaneously examining EL and EA as potential processes of change on an ongoing basis throughout the course of ACT. Three university students who endorsed mental health concerns associated with elevated levels of EA participated in the present study and received the proposed 10-week ACT intervention. Results of daily measured primary outcomes (i.e., clinically relevant behavioral excesses and deficits) and process of change variables (i.e., EL and EA), along with weekly and pre-, mid-, post-treatment, and 3-month follow-up self-report measures, provided equivocal support for the efficacy of the ACT intervention. Similarly, cross-lagged correlation analyses did not reveal evidence of temporal precedence of change in process over outcome variables (or vice versa), although these findings are still consistent with an ACT theory of behavior change. Further research should continue to examine the processes of change (and their temporal sequencing) within ACT for transdiagnostic mental health concerns, as well as the relationship between process of change variables and behavioral outcomes more generally.