Differential between-therapist effects in more versus less standardized therapies for depression

Psychotherapists can differ in their effectiveness. Yet, more research is needed to determine the generalizability of between-therapist effects to cultures beyond the US and UK, and whether these effects differ by treatment context. Addressing these gaps, we examined therapist effects in a randomized trial comparing cognitive behavioral therapy (CBT) versus psychodynamic therapy (PDT) for depression in the Netherlands, hypothesizing that therapists would explain significant outcome variance across both treatments. We also explored whether the size of therapist effects differed by degree of treatment standardization; in this trial, CBT was structured and manualized, whereas PDT was flexible and principle driven. Patients were 254 adults who received 16 sessions of CBT or PDT from 59 therapists nested within the condition. As predicted, multilevel models revealed significant therapist effects (explaining 3-8% of variance) on patient depression and general distress outcomes. Moreover, PDT therapists (10-16%) accounted for more outcome variance than CBT therapists (2-6%), though differences were only statistically significant for the clinician-rated depression outcome. Results extend the cultural "reach" of therapist effects. Moreover, they highlight treatment standardization as one possible determinant of effectiveness differences, which necessitates determining for which therapists such standardization is most important for optimizing their patient's outcomes.