Let’s define “work” simply as of perceived benefit to the individual. In a previous Scientific Encounters post, I provided “percentage of variability of outcomes” in psychotherapy - care of Laska and Gurman (2014) and Lambert and Bergin (1994).

Here they are again:

Factors common to all effective therapies: 43%

Differences between treatments - <1.0

Specific ingredients of therapies and treatments - 0.0

Adherence to protocol - <0.1

Rated competence in delivering particular treatment0.5

Extra-therapeutic events: 40%

Placebo effect (expectations): 15%

Per Laska and Gurman, “common factors” are those that are “necessary and sufficient for change: (a) an emotionally charged bond between the therapist and patient, (b) a confiding healing setting in which therapy takes place, (c) a therapist who provides a psychologically derived and culturally embedded explanation for emotional distress, (d) an explanation that is adaptive (i.e., provides viable and believable options for overcoming specific difficulties) and is accepted by the patient, and (e) a set of procedures or rituals engaged by the patient and therapist that leads the patient to enact something that is positive, helpful, or adaptive.” (p. 469)

Given that trust in a therapist and an “adaptive” explanation create expectations of improvement, it seems to me that the distinction between common factors and the placebo effect is somewhat arbitrary and artificial. Be that as it may, the picture in clear: subtract common factors, placebo effect, and life events, and the actual type of therapy doesn’t seem to matter all that much.

I don’t quite buy it. Partly because separating out the variables in such a clean-cut way is devilishly hard. For instance, did the authors of these studies distinguish between “extra-therapeutic events” that were probably independent of therapy, such as inheriting a ton of money, and those that may have come about, at least in part, because of therapy, such as finding a soul mate. After all, certain behaviors make certain events more or less likely and therapy often targets behavior and the things that influence behavior, like anxiety, social competence and self-confidence.

It may be that successful therapies work not only because of the common factors and  placebo effect but because they include specific ingredients that make it more likely beneficial life events will occur. The efficacy of these ingredients may be hard to detect, because their effects vary according to the person and situation. Some approaches/skills/strategies are useful for some individuals and situations but not for others - no one size fits all. But that isn't saying the effects aren't there.


Kevin M. Laska and Alan S. Gurman Expanding the Lens of Evidence-Based Practice in Psychotherapy: A Common Factors Perspective 2014, Vol. 51, No. 4, 467–481.

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.