A meta-analysis of common factor and specific treatment effects across the outcome domains of the phase model of psychotherapy.

A meta-analysis was conducted to determine whether the relative magnitude of common factor and specific treatment effects was related to the classes of outcome domain (subjective well-being, symptoms, and life functioning) described in Howard, Lueger, Maling, and Martinovitch's 1993 phase model of psychotherapy. Effect sizes were calculated for 80 outcome studies that each contained no-treatment, common factor, and treatment groups. Contrary to hypotheses, the magnitude of both (a) common factor versus no-treatment comparisons (r = .11) and (b) common factor versus specific treatment comparisons (r = .19) did not differ across domains. The magnitude of both components of psychotherapy was consistent across a variety of variables. A notable exception was the lack of significant common factor effects in the treatment of more severe disorders.