Palpacuer, C., Gallet, L., Drapier, D., Reymann, J-M., Falissard, B., & Naudet, Florian (2016). Specific and non-specific effects of psychotherapeutic interventions for depression: Results from a meta-analysis of 84 studies. Journal of Psychiatric Research.
Specific effect in psychotherapy refer to those technical interventions that are based on a treatment model that are specific to a particular modality. For example, the effects on symptoms caused by transference interpretations, cognitive restructuring, or exposure might all be considered specific effects. Non-specific effects is a very broad term that sometimes refers to effects on symptoms caused by common factors across all psychotherapies like therapist empathy, therapeutic alliance, or positive regard. Non-specific effects has also been used to refer to any extra-therapeutic effects that are more peripherally related to treatments, like type of control groups used in a study, researcher allegiance, number of treatment sessions, or length of follow-up. In this meta-analysis of 84 studies of over 6000 participants, Palpacuer and colleagues examined the association between non-specific factors (defined as intervention format [group or individual], client demographics, number of treatment sessions, length of follow up, and researcher allegiance to one of the treatment modalities) and treatment outcomes for depression. First, they looked at whether the specific type of intervention (cognitive behavioral, psychodynamic, interpersonal, problem solving, and others) was associated with reductions in depressive symptoms. Second, they assessed if the non-specific factors added to the prediction of improved depressive symptoms and accounted for some of the effects of specific types of interventions. Similar to previous findings, all psychotherapies were significantly more effective than waiting-list controls. However, the effects of the specific intervention approaches became non-significant when the non-specific factors were included in the analysis. That is, non-specific factors seemed to account for some of the effects of the specific treatments. In particular, if the study was conducted in North America vs Europe (β = 0.55, 95% CI: 0.22; 0.90), if the researcher had an allegiance to a particular therapeutic approach (β = 0.29, 95% CI: 0.07; 0.52), or if the number of sessions was higher (β = 0.03, 95% CI: 0.01; 0.04) then depressive outcomes were better.
This meta analysis of over 87 studies suggests that although various psychotherapies are effective, there remain questions about how and why they work. For example, the findings suggest that North American patients may have different expectations and higher responses to treatment, that a researcher's belief in the effectiveness of their favored intervention actually improves patients' outcomes, and that a higher number of sessions may also result in better outcomes. These factors appear to account for an important proportion of the specific effects of each type of psychotherapy.