Identifying the Underlying Mechanisms of Change During Acceptance and Commitment Therapy (ACT): A Systematic Review of Contemporary Mediation Studies

Abstract

Background: Mediation studies test the mechanisms by which interventions produce clinical outcomes. Consistent positive mediation results have previously been evidenced (Hayes et al., 2006) for the putative processes that compromise the psychological flexibility model of acceptance and commitment therapy (ACT). Aims: The present review aimed to update and extend the ACT mediation evidence base by reviewing mediation studies published since the review of Hayes et al. (2006). Method: ACT mediation studies published between 2006 and 2015 were systematically collated, synthesized and quality assessed. Results: Twelve studies met inclusion criteria and findings were synthesized by (a) the putative processes under investigation, and (b) the outcomes on which processes were tested for mediation. Mediation results were found to be generally consistent with the psychological flexibility model of ACT. However, studies were limited in methodological quality and were overly focused on a small number of putative processes. Conclusions: Further research is required that addresses the identified methodological limitations and also examines currently under-researched putative processes.

Psychological Flexibility in Depression Relapse Prevention: Processes of Change and Positive Mental Health in Group-Based ACT for Residual Symptoms

“…To understand the mechanisms through which ACT works, investigating PF, its processes, and their relationship to therapeutic outcome is necessary (Kazdin, 2007). A recent meta-analysis focusing on clinical studies found PF to mediate improvement in different aspects of mental health (Stockton et al, 2019). They found mediational evidence for the process of acceptance to be sound and thoroughly documented.…”

“…A broad exploration of the processes in ACT is needed to determine and refine which ones are central for change to occur (Hofmann and Hayes, 2019). There is a particular lack of clinical studies with long follow-ups that have examined the relative contributions of PF subprocesses as putative mechanisms of change in ACT (Stockton et al, 2019). Research responsive to this omission may have both conceptual as well as clinical practice implications.…”

Measuring psychological flexibility in youth with type 1 diabetes

“…16 While it can be trait-like for some individuals, psychological flexibility is posited to be context specific and is amenable to change through intervention, with recent evidence suggesting that the mechanism by which ACT works to improve outcomes is (in part) by increasing psychological flexibility. 17,18 ACT describes six core processes that comprise the psychological flexibility model. In addition to fostering flexible attention to the moment, values, committed action, self-as-context, and cognitive defusion, increasing acceptance (conceptualized as the opposite of experiential avoidance) is considered a key component of ACT.…”

A clinical effectiveness trial comparing ACT and CBT for inpatients with depressive and mixed mental disorders

“…The reason why we did not find an effect may have been because ACT does not focus on symptom reduction, instead improvement in symptoms is considered a by-product of psychological flexibility. Future research should include measures of the ACT process variables in order to test whether they have an indirect effect on general symptom reduction (Stockton et al, 2019).…”