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Yes, There Are Factors Common to All Effective Psychotherapy

Qualities like genuiness and empathy are real, and they are therapeutic.

ג'ון טניאל. (derivative work by user:אילילה) [Public domain]/Wikimedia Commons
Alice and Dodo
Source: ג'ון טניאל. (derivative work by user:אילילה) [Public domain]/Wikimedia Commons

In 1936, researcher Saul Rosenweig argued that factors common to different therapy models have a greater importance to client outcome than the model itself. He used the term “Dodo bird” as a sideways reference to Alice in Wonderland in which a number of characters had become wet, and a Dodo bird proposed a race in which they would all run around until they were dry. No one had prepared any good way to measure a winner. It remained unclear how far each had run or for how long, or who had become driest and when. The Dodo bird proclaimed, “Everybody has won and all must have prizes.”

Saul Rosenweig proclaimed back in the 1930s that the only data available indicated that psychotherapies were effective to certain extents but that there was not a significant discrepancy between how effective one therapeutic approach was versus another. Psychotherapy researchers ever since have battled to either overturn or support Rosenweig’s hypothesis, which remains highly controversial.

Since then, researchers have conducted studies that paint a clearer picture of what common factors psychotherapies share. In 1990, Grencavage and Norcross identified 35 specific “common factors.” In 1992, researcher Michael Lambert estimated on the basis of meta-analytic data that “extratherapeutic” factors having nothing to do with formal therapeutic work account for roughly 40% of therapeutic progress, that therapeutic relationship factors account for roughly 30%, client expectation or mindset and what is known as “the placebo effect” account for roughly 15%, and techniques unique to specific therapy models account for roughly 15%. These studies sparked a new wave of interest and engagement in research on common factors.

Haley Lawrence/Unsplash
Source: Haley Lawrence/Unsplash

Common factors remain hotly contested. It is widely accepted that there are factors common to different therapeutic approaches that contribute to therapy progress; what is contested is the degree to which the common factors influence therapy outcomes. Common factor theorists contend that common factors are causal agents in therapeutic work. These theorists do not disregard particular schools or modalities; to the contrary, what is acknowledged at this point by nearly all is that, in fact, psychotherapists tend to better employ these common factors in their work when they operate from a coherent model which provides a framework for understanding and intervening with client problems.

The Dodo research battle over the years has resulted in at least this certainty: Nothing works for everyone. Therapists and clients alike need choice: Although ultimately there may exist common factors contributing to therapeutic effectiveness across different models of therapeutic work, empirical evidence indicates that not all therapeutic approaches work equally well for all therapists or for all clients. Again, unique models and approaches are important, and it would be impossible to devise a therapeutic modality based on "common factors."

Mark Hubble, Barry Duncan, and Scott Miller (1999), themselves assertive spokesmen for the role of common factors, wrote:

"There is no reason for those who are devoted to the development and testing of specific techniques to discount the obvious benefits of common factors and particularly the importance of therapist attitudes of respect, caring, understanding, and concern. By the same token, those of us who are convinced of the primary importance of the therapist, as a person, would be well served by remaining open to the likelihood that specific techniques, when offered within the safety of the therapeutic relationship, will appreciably add to the therapeutic encounter."

"Alice in Wonderland"/Wikimedia Commons
"Alice in Wonderland," illustration from the book Boys and Girls of Bookland (1923), Smith & Smith/Wikimedia Commons
Source: "Alice in Wonderland"/Wikimedia Commons

Most common factors researchers agree common factors are real, therapeutic, and perhaps necessary but not sufficient in and of themselves to result in positive treatment outcomes. That being said, it should again be noted that a great deal of extratherapeutic factors contribute to therapeutic change, so-called, that are not clinical. In fact, faith, hope, relationships, and an unfathomable number of other factors impossible to quantify or procedurize, many external to the clinical enterprise, may catalyze therapeutic transformation.


Grencavage, L. M., & Norcross, J. C. (1990). Where are the commonalities among the therapeutic common factors? Professional psychology: Research and practice, Vol 21 (5), 372-378.

Hubble, M., Duncan, B., & Miller, S. (1999). The heart and soul of change: What works in therapy. Washington, D.C.: American Psychological Association.

Rosenzweig, S. (1936). Some implicit common factors in diverse methods of psychotherapy. American Journal of Orthopsychiatry, 6, 412–415.

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