Associations Between Treatment Adherence-Competence-Integrity (ACI) and Adult Psychotherapy Outcomes: A Systematic Review and Meta-Analysis

What is the public health significance of this article? This contemporary and comprehensive review of the body of evidence on the relationship between adherence/competence/integrity and clinical outcomes in adult psychotherapy indicates that competence and integrity are significantly related to clinical outcomes. Treatment integrity is a composite concept, referring to adherence to treatment procedures (with a clear differentiation from other approaches) in the context of skillful delivery of clinical methods. This meta-analysis offers empirical support for the need to ensure that psychological treatments are delivered in a theoretically consistent manner (therapist adherence), but with due attention to therapist interpersonal and relational skills (therapist competence). The integrity construct requires further conceptual clarification and more well conducted studies in naturalistic settings. Objective: To provide a comprehensive assessment of the association between psychological treatment adherence/competence/integrity (ACI) and clinical outcomes. Method: The review protocol was preregistered (CRD42020193889). Studies that assessed ACI-outcome relationships for adult psychotherapy were searched across three databases (Scopus, PsycINFO, MEDLINE). Random effects meta-analyses were conducted on adherence-outcome, competence-outcome, and integrity-outcome relationships. Separate analyses were performed for studies with hierarchical (i.e., patients nested within therapist) versus nonhierarchical study designs. Moderator analyses were performed according to predefined clinical and methodological features. GRADE assessments rated the quality of each meta-analytic comparison. Results: The review identified 62 studies suitable for inclusion (45 adherence-outcome, 39 competence-outcome, and seven integrity-outcome effect sizes; N = 8,210 across all analyses). No significant adherence-outcome association was found. A small significant positive association was found only in nonhierarchical studies between competence and outcome, r = 0.17, 95% CI [0.07-0.26], p < .001, similar to d = .34, GRADE = moderate. Small-to-moderate significant positive associations between integrity and outcome were found for both nonhierarchical, r = 0.15, 95% CI [0.06-0.23], p < .001, similar to d = .30, GRADE = high, and hierarchical study designs, r = 0.23, 95% CI [0.01, 0.43], p < .044, similar to d = .47, GRADE = low. Diagnosis, treatment modality and year of publication significantly moderated the strength of ACI-outcome correlations. Conclusions: Competence and integrity are significantly associated with clinical outcome, with a magnitude comparable to wider common factors. Further research is required to study these process-outcome associations with greater precision in routine-care settings and to understand the role of moderating variables.