This appendix outlines results of a study of the effectiveness of a ten-week group therapy ACT protocol for interpersonal problems. (The protocol used was the basis for the approach outlined in appendix C.) The randomized, controlled study, conducted by Avigail Lev at the Wright Institute, used the protocol with a group of forty-four male clients at a community-based clinic for recovery from substance abuse in Berkeley, California. Participants were assigned to one of two groups: treatment as usual (consisting of 22 participants) and the ten-week protocol plus treatment as usual (22 participants). (Treatment as usual was a day-treatment recovery program that included 12-step study, relaxation training, anger management, relapse prevention, and a host of other services.) The Inventory of Interpersonal Problems (IIP-64; Horowitz, Alden, Wiggins, & Pincus, 2000) was used as an assessment tool before and after the ten-week treatment program.
Researchers looked at several hypotheses, but the main hypothesis of this study was that ACT treatment would result in a reduction of maladaptive interpersonal functioning as compared to treatment as usual. This hypothesis was tested via an examination of participants’ pre- and post-treatment scores on the IIP-64. The table at the end of this appendix compares pre- and post-treatment test scores for participants in the treatment versus control group. (As a side note, the IIP-64 demonstrated excellent internal consistency, with Cronbach’s a = 0.96 at post-treatment, consistent with prior research.)
A mixed factorial analysis of variance (ANOVA) was performed to examine whether participants in the treatment versus control group exhibited differential changes in their IIP-64 scores over time. Overall, there was a main effect of assessment time, such that participants had lower IIP-64 scores at the post-treatment assessment (M = 1.20, SD = 0.63) as compared to the pre-treatment assessment (M = 1.45, SD = 0.66), F(1, 42) = 13.074, p < 0.01, ² = 0.237. The effect size indicates that assessment time explained 23.7 percent of the variance in IIP-64 scores. This main effect is qualified, however, by a significant interaction between experimental group and assessment time, F(1, 42) = 18.35, p < 0.001, ² = 0.304, such that participants in the ACT condition group exhibited a significant decrease in IIP-64 scores from pre-treatment (M = 1.64, SD = 0.66) to post-treatment (M = 1.09, SD = 0.62), t(21) = 5.41, p < 0.001, while control group scores did not change significantly from pre-treatment (M = 1.27, SD = 0.62) to post-treatment (M = 1.31, SD = 0.64), t(21) = –0.486, p = 0.63, ns. Participants did not differ significantly on their IIP-64 scores by group, F(1, 42) = 1.84, p = 0.67, ns, indicating that the two samples were matched on their levels of maladaptive interpersonal functioning prior to treatment. The effect size of the interaction term indicates that the interaction between treatment group and assessment explained 30.4 percent of the variance in IIP-64 scores. This effect size can be considered quite large (J. Cohen, 1988), implying that the ACT treatment resulted in a large and potentially meaningful reduction of participants’ maladaptive interpersonal functioning, beyond the reduction in these behaviors in the control group.
An independent samples t-test comparing the pre- and post-treatment IIP-64 score differences between the two treatment groups supported the hypothesis that participants in the ACT treatment group (MPost – MPre = –0.55) would exhibit a greater reduction in maladaptive interpersonal functioning as compared to those in the control group (MPost – MPre = 0.05), t(42) = –4.28, p < 0.001, d = –1.23. The Cohen’s d represents quite a large effect size and indicates that the difference between the mean scores for the treatment group is 1.23 standard deviation units larger than the difference between the mean scores for the control group.
In sum, the main hypothesis was supported by the data from the IIP-64. Participants who completed a ten-week ACT treatment exhibited greater improvement in their interpersonal functioning as compared to participants in the control group. Given prior research establishing empirical support for ACT treatment for a wide variety of psychological problems (see Ruiz, 2010), these results are quite promising for the treatment of interpersonal problems, although caution must be used in the interpretation of these data, given the small sample size.
Inventory of Personal Problems (IIP-64)
|ACT + TAU||TAU (control group)|
Note: Negative difference scores indicate a reduction in problem behaviors from pre-treatment to post-treatment.