Examining therapist effects in the alliance-outcome relationship: A multilevel meta-analysis

The relationship between the therapeutic alliance and outcome has been supported consistently over time. More recently, studies have examined therapist effects in the alliance-outcome relationship and came up with somewhat mixed findings. The purpose of this study was to replicate and extend previous meta-analytic work using a much larger data set, permitting not only the verification of the overall impact of the therapists' contribution but, at the same time, controlling for several potential covariates effecting this relationship.

We conducted two- and three-level mixed-effects meta-analyses (k = 152; 827 total effect sizes) to examine the significance of several potential moderators of the alliance-outcome correlation. These moderators included (a) Patient-Therapist Ratio (PTR; Patient N divided by therapist N to test therapist effects), (b) Alliance and Outcome Rater's contribution (patient, therapist, observer, and other), (c) Alliance Measures, (d) Research Design (RCT, Other) and (e) Personality Disorder.

The PTR, an index of the therapist's contribution to the alliance, was a significant moderator of the alliance-outcome correlation in both the two- and three-level models. When several potential confounds were simultaneously tested in a three-level multipredictor metaregression, including rater of alliance and outcome, research design, alliance measure, and personality disorder, PTR remained a significant moderator of the alliance-outcome correlation.

Replicating and extending previous research, this study supported the significance of therapists' impact in the alliance-outcome relationship. These results remained significant even when, using three-level metaregressions, several potential covariates were simultaneously controlled. (PsycInfo Database Record (c) 2021 APA, all rights reserved).