A bunch of studies have concluded that effective psychotherapy is almost entirely associated with factors common to all therapies but specific to none (Laska & Gurman , 2014; Wampold, 2015; Cuijpers, Reijnders, et al.; 2019). These common factors include:

Collaboration: the therapist and patient agree on treatment goals, approach and tasks.

Alliance: a confiding relationship and emotionally-charged bond between therapist and patient.

Empathy: the therapist is able to adopt the patient’s perspective and share the patient’s emotional state.

Positive Regard: the patient feels liked and respected by the therapist.

Belief Congruence: the therapist’s narrative, explanations, rituals, and assignments make sense to the patient and are consistent with the patient’s personal and cultural beliefs.

Expectations: the patient expects some benefit from therapy.

Therapist Effects: some therapists consistently achieve better outcomes than others, regardless of patient characteristics or the treatment delivered.

In contrast to common factors, there are specific factors associated with different types of therapy, such as the efficacy of a therapy’s particular ingredients. According to some meta-analyses, these specific factors account for less than 5% of the variability of outcomes in psychotherapy (Laska & Gurman, 2014; Wampold, 2015). What that means is that it doesn’t make much difference if you’re doing Cognitive-Behavioral, Interpersonal, Behavioral Activation, or Psychodynamic therapy. What matters much more is that you’ve got a good therapist who provides a plausible narrative for your troubles and gives you hope.

However, what makes for effective therapy is a different question than what accounts for successful therapy outcomes. Sure, common factors are important, but life events that happen independent of therapy also matter. One study (Lambert & Bergin, 1994) estimated that around 40% of the variation of psychotherapy outcomes could be attributed to these “extra-therapeutic” events. For example, it’s long been known that fresh-start experiences, such a getting a new job or partner, predict remission from depression (Harris, Brown, & Robinson, 1999).

A note of caution: to say that “x accounts for y” implies a casual relationship but the research on therapy outcomes is largely correlational (Cuijpers, Reijnders, et al., 2019). And correlation is not causation. Correlation is an arrow pointing to the need for more research. In the case of common factors and therapy outcomes, what’s needed to show a causal relationship is a better understanding of how these factors work their (apparent) magic on the human psyche.

References

Cuijpers, P., M. Reijnders, et al. (2019). "The Role of Common Factors in Psychotherapy Outcomes." Annual Review of Clinical Psychology 15(1): 207-231. https://doi.org/10.1146/annurev-clinpsy-050718-095424

Harris, T., Brown, G., & Robinson, R. (1999). Befriending as an intervention for chronic depression among women in an inner city: 2: Role of fresh-start experiences and baseline psychosocial factors in remission from depression. British Journal of Psychiatry, 174(3), 225-232. doi: https://doi.org/10.1192/bjp.174.3.225

Lambert, M. J., & Bergin, A. E. (1994). The effectiveness of psychotherapy. In A. E. Bergin & S. L. Garfield (Eds.), Handbook of psychotherapy and behavior change  (4th ed., pp. 143–189). New York, NY: Wiley.

Laska, K. M. & Gurman, A. S. (2014) Expanding the Lens of Evidence-Based Practice in Psychotherapy: A Common Factors Perspective 2014, Vol. 51, No. 4, 467–481. https://doi.org/10.1037/a0034332

Wampold, B.E. (2015), How important are the common factors in psychotherapy? An update. World Psychiatry, 14: 270-277. doi:10.1002/wps.20238