Stevens, Hynan, and Allen meta-analyzed 80 psychotherapy outcome studies; with each study containing a no-treatment control, a common factor control, and a full treatment group. It was hypothesized that the relative magnitude of common factor and specific factor ESs would be moderated by the outcome domains of the phase model of psychotherapy (Subjective Well-being, Symptoms, and Life Functioning). All ESs were calculated as r, which is usually .5 x d. Unless otherwise noted, all ES listed below are sig, p < .05

Overall Results:

Common factor ES = .11: Common factor control – No treatment

Specific factor ES = .19: Complete treatment – Common factor control

Complete treatment ES = .28: Complete treatment – No treatment

ESs were not moderated by phase model outcome domain, reactivity of measure, common factor credibility, or treatment length. ESs were moderated by severity of disorder (Chronic/characterological vs. Acute/circumscribed): Common factor/more severe, ES = .05, ns: Common factor/less severe, ES = .18: Specific factor/more severe, ES = .18; Specific factor/less severe, ES = .19.

Conclusions:

The relative magnitude of specific to common factor ESs is larger than that reported in previous meta-analyses, which usually show both components having relatively equal magnitude.

Limitations: There is great heterogeneity in the common factor controls, and some common factor controls may have been designed as week conditions. In light of this limitation, Study 2 was conducted.

Study 2 was a meta analysis of 33 studies, each containing at least one “more complex” complete treatment and one “less complex” treatment. 15 of the 33 studies contained a no treatment group. “Less complex” treatments were either Progressive Muscle Relaxation or Biofeedback.

Hypotheses: That “less complex” treatments, which contain common factors of skills acquisition in the context of a helpful relationship, would have a significantly larger common factor ES than that observed in Study 1. Also, “Is psychotherapy more beneficial than scuba lessons with Mr. Rogers?”

Results:

Less complex ES = .19: less complex treatment – no treatment

More complex ES = .08: more complex treatment – less complex treatment

Complete treatment ES = .25: More complex treatment – no treatment

Limitations:

Many of the studies in Meta-analysis 2 are limited to treatments of physiological and psychosomatic disorders.