Is Alliance Therapeutic in Itself? It Depends

The alliance has been a leading player in the long-running debate on whether therapeutic change is driven by factors common across distinct treatments or by treatment-specific factors. The present study disentangled between-patients differences in alliance strength from within-patient changes to investigate whether two treatments with identical goals but based on different roles of alliance differ in the within-patient effect of alliance on outcome. Both treatments are aimed at improving the patients' interpersonal abilities, but in the supportive treatment (ST) the alliance is the main specific factor, whereas in the supportive-expressive treatment (SET) it is conceptualized as a common factor. One hundred patients were randomized to receive either ST or SET. Treatment outcome and alliance were assessed weekly. Treatment condition significantly moderated the effect of within-patient changes in the alliance (relative to its mean) on subsequent treatment outcome, so that any increases in state-like alliance predicted lower levels of subsequent depressive symptoms in ST than in SET. Public Significance Statement Findings suggest that within-patient changes in the alliance (relative to its mean) result in better treatment outcome in a treatment that focuses on the alliance as a main mechanism of change than in a treatment that does not. The findings support the theoretical assumption that different treatments work through distinct mechanisms, marking another step forward toward precision mental health.