Let's face facts: Common factors are more potent than specific therapy ingredients

Luborsky et al.'s findings of a nonsignificant effect size between the outcome of different therapies reinforces earlier meta-analyses demonstrating equivalence of bonafide treatments. Such results cast doubt on the power of the medical model of psychotherapy, which posits specific treatment effects for patients with specific diagnoses. Furthermore, studies of other features of this model-such as component (dismantling) approaches, adherence to a manual, or theoretically relevant interaction effects-have shown little support for it. The preponderance of evidence points to the widespread operation of common factors such as therapist-client alliance, therapist allegiance to a theoretical orientation, and other therapist effects in determining treatment outcome. This commentary draws out the implications of these findings for psychotherapy research, practice, and policy.