Acceptance and commitment therapy (ACT) is based on the psychological flexibility model, which includes a therapeutic process referred to as “self-as-context” (SAC). This study investigates whether ACT is associated with an effect on SAC and whether this effect is linked to treatment outcomes in people with chronic pain. Four hundred twelve adults referred to a pain management center participated in the study. Participants completed measures of treatment processes (SAC, pain acceptance) and outcomes (pain-related interference, work and social adjustment, depression) before treatment, upon completion of treatment, and at 9-month follow-up. Paired sample t-tests and analyses of meaningful change were conducted to examine changes in processes and outcomes. Regression analyses with residualized change scores from process and outcome variables, and bivariate growth curve modeling were used to examine the association between change in SAC and change in outcomes. Participants significantly improved on all process and outcome variables at post-treatment (d = .38–.98) and 9-month follow-up (d = .24–.75). Forty-two to 67.5% of participants showed meaningful improvements on each outcome at post-treatment and follow-up. Change in SAC was associated with change in outcomes (β = −.21 to −.31; r = −.16 to −.46). Results support a role for change in SAC in treatment as the psychological flexibility model suggested.
