The search for common factors in psychotherapy: Two theoretical models with different empirical implications

The difficulties of demonstrating that any specific form of psychotherapy is more effective than any other has led to the formulation of the so-called Dodo Bird Verdict (that all forms of therapy are equally effective) and to the suggestion that what really matters for therapeutic efficiency are factors that are common to different forms of therapy. The term “common factors”, however, is seldom defined in an unambiguous way. In this paper, two different models of “common factors” are differentiated, and their implications are compared. The first model is referred to as the Relational-Procedural Persuasion (RPP) model and is primarily based on the writings of Frank and Wampold; according to this model effective psychotherapy requires a good therapeutic relationship, a specified therapeutic procedure, and a rhetorically skilful psychotherapist who persuades the client of a new explanation that provides new perspectives and meanings in life. The contents of these procedures and perspectives, however, are less important – according to this model, the treatment procedures are beneficial to the client because of the meaning attributed to these procedures rather than because of the specific nature of the procedures. The other model, the Methodological Principles and Skills (MPS) model, is based on the assumption that effective psychotherapy relies on common methodological principles that are instantiated in various ways in different forms of psychotherapy, and on the therapist’s capacity of applying these principles in a skillful way. According to this model, method matters, and it is possible to improve existing methods. Whereas the MPS model carries a hope for the improvement of psychotherapy, the RPP model implies a more pessimistic view of psychotherapy as forever bound by the limits of the Dodo Bird Verdict. It is concluded that psychotherapy research may benefit from using the MPS model as a working hypothesis, but that a comprehensive model of common factors in psychotherapy also needs to integrate important insights from the RPP model, as well as an understanding of the structural characteristics that psychotherapy shares with other kinds of social interaction.