Associations of Group Size with Cohesion and Clinical Outcomes in Group Psychotherapy: A Systematic Review.

Group size is a consideration for all psychotherapy groups, yet the topic has been subject to surprisingly few empirical investigations. This review explored the influence of group size within group psychotherapy by investigating its associations with cohesion and clinical outcomes. Significant group-size associations were found in seven of the 17 included individual and meta-analysis studies (combined N = 21,425), pointing to partial support for the influence of group size. Some interesting tentative trends were identified, such as potentially better outcomes in smaller groups and greater group-size influence in process-orientated groups. Considerably more research is needed, as psychotherapy group-size decisions should ideally be informed by empirical evidence rather than by relying on clinical opinion, conventional wisdom, and recommendations made by influential commentators.