Common factors theory

Common factors theory in psychotherapy
Within psychotherapy research, common factors theory proposes that different theoretical and evidence-based approaches to psychotherapy and counseling have common components and that those components account for outcome more than components that are unique to each approach. This is in opposition to the medical model, which proposes that the efficacy of psychotherapy is because of specific, critical ingredients in treatment for specific problems (Imel & Wampold, 2008). Based on studies that combine the results of as many psychotherapy outcome studies, it seems that there is no significant difference between various common psychotherapy approaches in terms of client outcome. This is known as the "Dodo-bird Hypothesis," so-named after a scene in Alice in Wonderland when, after the characters race and everyone wins, the Dodo bird says, "everyone has won, so all must have prizes."

It is important to clarify that the term psychotherapy is most commonly used in the sources cited, but common factors theory also applies to counseling. The literature and implications for common factors theory span counseling and psychotherapy.

Common factors theory predicts that different psychotherapy treatments lead to similar outcomes, and that different treatments have similar underlying components that contribute to outcome (Imel & Wampold, 2008). Studies that test common factors theory tend to investigate possible differences in outcomes in psychotherapy efficacy studies, and the nature of the approaches being compared.

Eysenck's study on the efficacy of psychotherapy found that psychotherapy generally did not seem to lead to improved client outcomes. Numerous studies later showed substantial evidence in support of the general efficacy of psychotherapy, ). There is also evidence that different approaches to psychotherapy tend to be similar in terms of outcome (Wampold, 1997). It is possible that specific disorders might require specific types of treatment, but so far comparisons between treatments for different disorders have not shown the superiority of one treatment over another (Imel & Wampold, 2008).

It is also possible that different approaches are equally effective but still distinct in their mechanisms for client change. Therefore, methods for testing common factors theory use a variety of methods for comparing psychotherapy studies. One method used involves comparing placebo or common factor control groups to treatment groups. Another method involves testing specific components within a theory or approach, such as by comparing a behavioral therapy with a cognitive-behavioral therapy (Imel & Wampold, 2008). Finally, if a specific aspect to treatment is critical for successful outcomes, then therapists' adherence to a type of treatment should be related to outcome. From the hundreds of studies using such methods, there is no evidence that one type of psychotherapy is reliably better than another (Imel & Wampold, 2008).

The Common Factors
There are several models of common factors. One empirically-derived model proposes two dimensions (thinking and feeling) and three clusters: bond, information, and role. Studies suggest that 30% to 70% of therapy outcome is due to common factors (Imel & Wampold, 2008).

Criticisms of Common Factors Theory
One criticism of common factors theory is that though all the factors are necessary, they are not sufficient for client change. The theory does not account for techniques and therapist behavior. Another criticism is that common factors are nothing more than a good therapeutic relationship, though Imel & Wampold suggest that, though the therapeutic relationship is important, it is not the only common factor. Finally, some feel that common factors theory is not scientific, especially in comparison to the medical model.