[The Effect of Therapists' Interpersonal Skills on Therapeutic Alliance]

Therapists' interpersonal skills play a significant role in outcome differences between therapists. Similarly, the strength of the therapeutic alliance is influenced by therapist characteristics. Therefore, the aim of this study was to capture therapist differences in the alliance and to examine the effect of therapists' interpersonal skills on the therapeutic alliance.

Interpersonal skills of 99 incoming therapists were measured in a group discussion using the Therapy-Related Interpersonal Behaviors (TRIB) scale. The therapists treated n=1031 psychotherapy outpatients as part of their clinical training. The alliance was assessed at the end of therapy using the Assessment for Signal Clients (ASC). Hierarchical linear models were used to predict the alliance from interpersonal skills, controlling for other patient and therapist variables. Initial impairment was examined as a moderator of the effect.

The therapist effect (TE) on the alliance was 7.3%. Interpersonal skills were a significant predictor of the alliance (b=0.104, p<0.001) and could explain 1.8% of the total variance beyond all control variables. The TE was reduced to 5.7%, meaning that 23.0% of the therapist differences in the alliance could be attributed to interpersonal skills. Although the moderation effect of initial impairment was only marginally significant (b=0.069, p=0.061), the association between interpersonal skills and alliance disappeared with low patient impairment.

The TRIB scale can measure interpersonal skills before the start of training. The prediction should be considered in the context of the several years' temporal distance between the measurements of interpersonal skills and the alliance, applicable to the selective sample of therapists chosen for the training.

Interpersonal skills can predict the alliance. The influence of therapists' interpersonal skills on the alliance increases with the initial impairment of patients, while there is no significant relationship with low-impaired patients. Using video-based rating systems, interpersonal skills of individual therapists can be measured automatically, therapists with deficits can be identified, and targeted training can be provided.