Processes of Change in Acceptance and Commitment Therapy and Cognitive Therapy for Depression: A Mediation Reanalysis of Zettle and Rains

Several articles have recently questioned the distinction between acceptance and commitment therapy (ACT) and traditional cognitive therapy (CT). This study presents a reanalysis of data from Zettle and Rains that compared 12 weeks of group CT with group ACT. For theoretical reasons, Zettle and Rains also included a modified form of CT that did not include distancing, and no intent-to-treat analysis was included. Particularly because that unusual third condition did somewhat better than the full CT package, it contaminated the direct comparison of ACT and CT, which has of late become theoretically interesting. In the present study, data from participants in the ACT and CT conditions were reanalyzed. ACT was shown to produce greater reductions in levels of self-reported depression using an intent-to-treat analysis. Posttreatment levels of cognitive defusion mediated this effect at follow-up. The occurrence of depressogenic thoughts and level of dysfunctional attitudes did not function as mediators. This study adds additional evidence that ACT works through distinct and theoretically specified processes that are not the same as CT.