Common Factors Model

The study of psychotherapy has yielded important insights into the predictors of clinical improvement. One major focus of the psychotherapy outcome literature has been to determine the most efficacious treatment models or techniques. For example, is cognitive therapy (CT), in which therapists focus on helping clients identify and challenge irrational thoughts, more effective in treating depression than interpersonal psychotherapy (IPT), in which therapists encourage clients to discuss and troubleshoot problems in their social relationships?

Reviews indicate that the number of psychotherapies has increased approximately 600% since 1960 and the number of psychotherapeutic treatments models is greater than 200. Are each of these therapies fundamentally different, offering clients help in separate ways, or might they share more in common than one might expect? While proponents of the various models claim that techniques and strategies specific to their models account for client change, research indicates that the mechanisms responsible for change may not differ according to theoretical approach. The common factors theory stems from the contention that much of the effect of the various psychotherapies is due to factors that psychotherapies share, rather than those that are unique to a particular type of therapy. Researchers estimate that common factors account for between 45% and 70% of the effects of psychotherapy. This is in comparison to an upper bound of 8% accounted for by specific techniques.

The Dodo Bird

Seventy years ago, Saul Rosenzweig introduced the concept of common factors in what has become a classic article, noting that apparently diverse forms of psychotherapy appear to be similarly successful. Attempting to capture the peculiarity of this phenomenon, Rosenzweig invoked Lewis Carroll’s Alice in Wonderland, noting the dodo bird’s proclamation that “Everyone has won, and all must have prizes.” The finding that most psychotherapies tend to have similar rates of efficacy has subsequently been labeled the dodo bird conjecture.

Ironically, the empirical basis of common factors research was spurred by Hans J. Eysenck’s controversial outcome study, in which he found minimal, custodial treatment to be more effective than psychotherapy. In response to Eysneck’s work, researchers set about rigorously demonstrating the beneficial effects of psychotherapy. Mary L. Smith and Gene V. Glass used meta-analysis, a statistical method that allows for the findings of many research studies to be combined, to establish the therapeutic effect of psychotherapy. They combined the results of more than 375 studies and provided compelling evidence in support of the efficacy of psychotherapy. Subsequent meta-analyses have confirmed the efficacy of psychotherapy over no treatment. Most striking, however, is that meta-analytic findings are consistent with Rosenzweig’s original proposition that different psychotherapies have approximately similar effects. In the most extensive meta-analysis of psychotherapy treatment studies to date, Bruce E. Wampold and colleagues found no evidence of differential treatment effects.

This finding leads to a paradox. Treatments with different theorized mechanisms of change yield quite similar results. Thus, psychotherapies could be like radiation and chemotherapy, completely different, yet similarly effective treatments for the same illness.

Alternatively, they could be quite similar in their active ingredients, like two aspirin-containing pain relievers marketed under different brand names. Common factors researchers investigate hypotheses related to the latter.

The Common Factors

The lack of a consensual operational definition of the term common factors has posed a problem for researchers, and there are three widely cited organizational schemes for categorizing the factors. Rosenzweig’s original model included four common factors: (1) catharsis, (2) the personality of the good therapist, (3) the therapeutic ideology, and (4) the alternative formulation of psychological events. Julia D. Frank and Jerome B. Frank also listed four components as necessary: (1) a healer in whom faith is placed, (2) a conceptual scheme or myth consistent with the assumptive world of the client and therapist that makes sense of the symptoms, (3) a locality that is imbued with the power of healing (e.g., hospital, psychologist’s office), and (4) a task or procedure that demands effort and is a vehicle for maintaining the therapeutic relationship. The final organizational approach identifies five broad categories of common factors: (1) client characteristics, (2) therapist qualities, (3) the therapeutic relationship, (4) change processes, and (5) treatment structures. Although these categories are not mutually exclusive (e.g., therapist qualities are likely not independent of the quality of therapeutic relationship, and the therapeutic relationship may be considered a change process by some), this approach is useful for the purposes of succinctly describing the extant literature on common factors.

Therapist Factors

Although recent outcome research has primarily focused on determining the most effective treatments for specific groups of clients, reanalyses of these studies indicate that the therapist may be a more important factor in determining outcome than the type of treatment. On the average, the therapist accounts for approximately 6% to 9% of the variability in outcomes. This is in contrast to the variability among treatments, which is approximately 1% at most. This finding is consistent with the common factors hypothesis, since if the most important determinants of change are shared across therapies, then the qualities of the person implementing the therapy should be of more importance than variations in type of treatment.

Although the therapist appears important in determining psychotherapeutic change, empirically clarifying the qualities of an effective therapist has been a challenging task. This question remains important in regard to the common factors hypothesis. Although therapist variability may indicate that certain pantheoretical therapist characteristics are critical to helping clients, the finding that the therapist accounts for differences in client outcome may be related to differential skill in implementing or fidelity to a particular therapy’s techniques.

Findings consistent with the latter explanation noted above would be inconsistent with the common factors hypothesis and lend support to specific theoretical explanations of psychotherapy. However, treatment adherence, or the degree to which a therapist faithfully performs the techniques of a particular therapy (and does not perform the techniques of other therapies), has not consistently predicted clinical outcome. Furthermore, analyses indicate that therapist demographic variables (type of training, years of training, theoretical orientation) do not differentially contribute to client outcome. It is important to note how this differs from what one might expect in more traditional medical settings. For example, one would expect that a surgeon who more closely follows the accepted protocol for an appendectomy would be more successful than one who does not.

Instead, the most commonly cited beneficial therapist trait is the rather generic positive descriptors. More specifically, a recent meta-analysis demonstrated that client ratings of therapist empathy were significant predictors of therapy outcome, accounting for approximately 7% to 10% of variance in outcomes. Reanalyses from a large clinical trial indicate that more effective therapists: (a) tended to focus on the psychological versus biological aspects of depression, (b) were more likely to be psychologists than psychiatrists, (c) used psychotherapy only rather than in combination with medication, and (d) expected treatment to take longer. Thomas M. Skovholt and Len L. Jennings analyzed the interviews of 10 psychotherapists who were nominated by colleagues as master therapists and reported that such therapists described a number of common traits. Among these were descriptors such as (a) a desire for lifelong learning, (b) valuing cognitive complexity and ambiguity, (c) attention to their own emotional well-being and how it may influence their work, and (d) relational competence that is utilized in therapy. Although it remains unclear how these descriptors influence therapeutic change, it seems clear that therapist qualities that cut across convenient theoretical boundaries are among the most important predictors of psychotherapeutic change.

Client Factors

Although among the least cited factors, the characteristics of the client may be among the most important ingredients in effective therapy. Positive expectation and hope are the most frequently cited of these client factors. E. Fuller Torrey noted that faith in the institution (e.g., seeking treatment or merely walking in the door) may lead clients to improve.

Specifically, expectation can be operationalized as cognitions regarding the likelihood that an event will occur. A significant body of research has addressed the construct of client expectations, and findings confirm that expectancies are significant predictors of psychotherapy outcome. If clients believe they are likely to improve by engaging in therapy, they often do. Expectations about counseling have an important impact on decisions to begin or remain in psychotherapy and on the effectiveness of psychotherapy in general. Those with positive expectations are more likely to begin psychotherapy, invest more fully in the therapeutic process, remain in therapy even when it is difficult, and experience positive outcomes.

Relationship Factors

The relationship between therapist and client is the most widely cited and researched common factor, revealing robust findings and generating a significant body of literature. The genesis of the therapeutic alliance can be traced back to Sigmund Freud’s early papers in which he noted the importance of positive attachment between the analyst and the patient. In 1975, Edward S. Bordin formally presented the first pantheoretical notion of alliance in his presidential address to the Society of Psychotherapy Research. He argued that the alliance was composed of three related components: (1) bonds, (2) tasks, and (3) goals. Specifically, bonds referred to the interpersonal attachment in psychotherapy; tasks were the agreement surrounding what is to be done in therapy; and goals were the degree of consensus between therapist and client relative to long- and short-term outcome expectations. Recent meta-analyses indicate that measures of the therapeutic relationship derived from this construct are moderate predictors of treatment outcome. There is also evidence supporting the tear and repair hypothesis, which holds that therapeutic relationships that involve a period of decline (i.e., tear) that is followed by periods of improvement (repair) may actually be more indicative of successful therapy than therapeutic dyads with static or even steadily increasing relationship quality.

Researchers such as Carl R. Rogers held that the empathic bond between a client and therapist was sufficiently powerful to induce change in and of itself. In Rogers’s view, the role of the therapist is to facilitate a collaborative and genuine interpersonal relationship with the client and unlock the client’s own natural tendency toward growth and development. Psychodynamic theories (the most direct descendents of Freud’s psychoanalysis) include direct discussion of the relationship between client and therapist as the central ingredient central in successful therapy. More specifically, psychodynamic therapists contend that clients tend to repeat the maladaptive patterns of past relationships in the therapy session and that is the role of the therapist to make these patterns explicit so that they can be discussed openly and be changed.

Others, such as Aaron T. Beck, the founder of cognitive therapy, argued that an adequate therapeutic alliance is important in that it allows for the client and therapist to engage in the primary work of cognitive approaches, namely, examining the validity of irrational automatic thoughts and determining problematic cognitive schemas. Integrative therapists such as James P. McCullough, the developer of the cognitive-behavioral analysis system of psychotherapy (CBASP), have argued for a more robust discussion of the therapeutic relationship in cognitively oriented therapies.

Research provides no clear answers in regard to the respective validity of the above claims. Thus, it remains possible that the therapeutic relationship has an impact on clinical outcome in different ways across therapies (as suggested by the various theories above). However, it is important to note that, as yet, findings do not support significant differences in the effect of the therapeutic alliance in regard to therapy type (e.g., interpersonal, cognitive behavior, active, and placebo pharmacotherapy with clinical management). Consistent with the common factors hypothesis, this finding indicates that despite divergent theories regarding the therapeutic relationship, the mechanisms mediating its effects on clinical outcome may be quite similar.

Change Processes

Change processes are the means through which therapeutic change is thought to occur. Approximately 30 commonalities have been identified under this subheading, the most frequent of these being: (a) opportunity for catharsis, (b) acquisition and practice of new behaviors, (c) provision of rationale, (d) fostering insight/ awareness, and (e) emotional or interpersonal learning.

Numerous findings illustrate the importance of providing a therapeutic rationale that is acceptable to clients. The rationale addresses both the cause of the presenting concern and the approach chosen to address that concern. Participants prefer counseling theories that are congruent with their personal epistemology, and congruence of client worldview and psychotherapeutic theory is positively related to outcome.

Treatment Structures

Treatment structure is the specific implementation of the rituals and techniques particular to a certain treatment. All effective treatments have rituals and related techniques. The most frequently cited factors related to treatment structure are: (a) use of techniques/ritual, (b) a focus on the “inner world”/exploration of emotional issues, (c) adherence to theory, (d) interacting participants, (e) communication (verbal/nonverbal), and (f) explanation of therapy and participant roles. Research on treatment structures suggests that it does not matter which specific treatment approach is followed as long as the chosen approach includes the above factors. Thus, although evidence supporting the importance of specific structures or techniques is lacking, the presence of structure and techniques in general appears to be an important common factor.


  1. DeRubeis, R. J., Brotman, M. A., & Gibbons, C. J. (2005). A conceptual and methodological analysis of the non-specifics argument. Clinical Psychology: Science & Practice, 12, 174-183.
  2. Frank, J. D., & Frank, J. B. (1991). Persuasion and healing: A comparative study of psychotherapy (3rd ed.). Baltimore: Johns Hopkins University Press.
  3. Grencavage, L. M., & Norcross, J. (1990). Where are the commonalities among the therapeutic common factors? Professional Psychology: Research and Practice, 21, 374-376.
  4. Norcross, J. C. (2002). Psychotherapy relationships that work. New York: Oxford University Press.
  5. Rosenzweig, S. (2002). Some implicit common factors in diverse methods of psychotherapy. Journal of Psychotherapy Integration, 12, 5-9. (Original work published 1936)
  6. Skovholt, T. M., & Jennings, L. (Eds.). (2004). Master therapists: Exploring expertise in therapy and counseling. Boston: Allyn & Bacon.
  7. Smith, M. L., & Glass, G. V. (1977). Meta-analysis of psychotherapy outcome studies. American Psychologist, 32, 752-760.
  8. Wampold, B. E. (2001). The great psychotherapy debate. Mahwah, NJ: Lawrence Erlbaum.

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