Background: Group therapy is a popular and effective format for psychological intervention, and both anecdotal and empirical data consistently point to group dynamics as a primary driver of its benefits. However, to date there has been no systematic investigation of what facilitates an engaged, cohesive group environment. We argue that this is social identification and explore the features of groups that help to build this. Method: We present two longitudinal studies of group therapy and examine the predictors of social identification. Study 1 was a sample of psychiatric outpatients (N = 103) who completed group cognitive behavior therapy. Study 2 was a sample of young women with body shape or weight concerns (N = 112) who completed an eating disorder prevention program. Results: Multilevel analyses indicated that social identification was best predicted by participant fit with the therapy group, specifically the degree to which (1) participants were and perceived themselves to be similar to other group members, and (2) participants met the group therapy eligibility criteria at baseline. Conclusions: These results show that attending to issues of client fit in group therapy can improve social identification, with implications for reducing client attrition and improving client outcomes.
Keywords: group processes; group therapy; mechanisms of change; psychotherapy; social identity.