Therapeutic alliance as a mediator of change: A systematic review and evaluation of research

The alliance-outcome relationship has been consistently linked to positive treatment outcomes irrespective of psychotherapy modality. However, beyond its general links to favorable treatment outcomes, it is less clear whether the alliance is a specific mediator of change and thus a possible mechanism underlying psychotherapy response. This systematic review evaluated research examining the alliance as a potential mediator of symptom change, reviewing study characteristics of 37 relevant articles examining the alliance-outcome relationship and the extent to which these studies met recommended criteria for mechanistic research. Alliance mediated therapeutic outcomes in 70.3% of the studies. We observed significant heterogeneity across studies in terms of methodology, including timing of alliance assessment, study design, constructs used in mediation models, and analytic approaches. Building on recent methodological advancements, we propose directions for future research examining the putative mediational role of alliance, such as greater uniformity in and attention to study design and statistical methodology. This review highlights the importance of alliance in therapeutic change and discusses how adhering to requirements for process research will improve our ability to more precisely estimate how and to what extent alliance drives therapeutic change. •We evaluated studies examining the alliance as a mediator of change in psychotherapy.•Alliance plays an important role pantheoretically.•Studies displayed methodological and statistical heterogeneity.•Steps for improving future mediation research are proposed.