Group Dynamics: Theory, Research, and Practice, Vol 30(1), Mar 2026, 47-63; doi:10.1037/gdn0000247
Objective: Group psychotherapy provides a unique therapeutic context where individuals can model and practice interpersonal skills within a social microcosm. Research suggests that discrepancies in interpersonal styles among group members significantly influence group dynamics, processes, and outcomes. However, little is known about how discrepancies between an individual group member’s and other group members’ interpersonal styles impact group psychotherapy outcomes. Guided by the interpersonal complementarity theory and mutual influence theory, this study examined the effect of discrepancies in an individual member’s dominance (actor effect) and the other group members’ dominance (partner effect) on the individual member’s adjusted posttreatment psychological symptoms. Method: Data consisted of 201 clients participating in focused brief group therapy at a university counseling center between 2015 and 2019. Using the actor–partner interdependence model and polynomial regression with response surface analysis, we modeled pretreatment actor and partner dominance component as predictors of individual group members’ posttreatment outcomes. Results: Results indicated a significant positive congruent effect between actor dominance and partner dominance on an individual group member’s posttreatment outcome. In addition, there was a significant positive discrepant effect between actor dominance and partner dominance on an individual group member’s posttreatment outcome. Conclusions: These findings highlight the complex interplay between group members’ interpersonal styles and group composition, providing important implications for structuring and leading groups to optimize interpersonal growth in group psychotherapy. (PsycInfo Database Record (c) 2026 APA, all rights reserved)