Allegiance and treatment quality as moderators of the comparative effectiveness of psychotherapy? A systematic review and meta-analysis of studies comparing humanistic psychotherapy to other psychotherapy approaches

Background: Achieving positive outcomes in comparative RCTs examining psychotherapy interventions may be moderated by other factors than treatments alone, namely allegiance and treatment quality (bona fide, adherence). Using the study sample of a recent comprehensive review on humanistic interventions by the German Scientific Board of Psychotherapy, we assumed that higher allegiance towards non-humanistic approaches and lower treatment quality in the humanistic intervention arm would result in worse outcomes for the humanistic groups. Method: We included studies in which a humanistic psychotherapy (sub-)approach was compared to another type of psychotherapy. Data was extracted independently by the authors. A priori defined meta-regression analyses were performed with allegiance and treatment quality as main moderators and study quality (risk of bias), type of active control, humanistic psychotherapy and target population (children/adolescents; adults) as exploratory. Results: The majority of studies showed non-allegiance towards humanistic intervention arms; only about half of the humanistic interventions were bona fide treatments demonstrating high percentages of potential biases in these comparative intervention studies. However, allegiance and bona fide were significant moderators only for two (allegiance) resp. one (bona fide) of five outcome comparison. Type of active control (cognitive behavioural therapy) and disorder group (anxiety disorders) emerged as further moderators. Conclusion: We found no clear evidence for allegiance or treatment quality impacting upon treatment outcome in this re-examination. Allegiance and treatment quality were not as relevant for outcomes in this meta-analysis of RCTs as expected.