Are Therapist Effects More Crucial than We Thought?

One of the main limitations of routine outcomes psychotherapy studies is the lack of random assignment to treatment conditions, which precludes causal inference. At the same time, therapist effects and empirically supported therapy relationships have proven to be important and even more influential than the type of treatment. In this theoretical study, we propose using therapist effects estimation, which refers to the systematic differences in the effectiveness of improving patient outcomes between therapists, to mitigate this limitation. The theoretical rationale for treating different therapists’ treatments as different treatment conditions is presented in depth while referring to practical methods of examining therapist effects estimation at the individual sample level. The current study demonstrates how variation in the results obtained by therapists in field studies holds the potential to approximate a causal relationship between therapy and outcomes. In light of this, we recommend performing significance testing for the therapist effect in every psychotherapy study where this is possible, as well as advocating investing resources in the personal development of the therapist and giving room for clinical experience in decision-making.