Is there an allegiance bias on the efficacy of systemic therapy? A three-level meta- regression analysis

OBJECTIVE: Allegiance bias affects the reproducibility of psychotherapy outcomes, but its impact in systemic therapy (ST) remains largely unexplored. METHOD: Two meta-analyses were conducted: Study 1 with 42 RCTs (364 effect sizes) for children and adolescents, as well as Study 2 with 30 RCTs (161 effect sizes) for adults. Allegiance was measured using a comprehensive rating scale across researcher, therapist, trainer, and supervisor levels. Furthermore, risk of bias (RoB) was assessed using the adapted tool for psychotherapy. Three-level meta-regressions were performed, controlling for dosage. RESULTS: = 42). CONCLUSION: The findings underscore the role of researcher allegiance investigating ST for children and adolescents and RoB in ST for adults, highlighting the need for transparent methods and replication efforts.