Objective: Pharmacotherapy, cognitive-behavioral therapy (CBT), and psychodynamic therapy are most frequently applied to treat mental disorders. However, whether psychodynamic therapy is as efficacious as other empirically supported treatments is not yet clear. Thus, for the first time the equivalence of psychodynamic therapy to treatments established in efficacy was formally tested. The authors controlled for researcher allegiance effects by including representatives of psychodynamic therapy and CBT, the main rival psychotherapeutic treatments (adversarial collaboration).
Method: The authors applied the formal criteria for testing equivalence, implying a particularly strict test: a priori defining a margin compatible with equivalence (g=0.25), using the two one-sided test procedure, and ensuring the efficacy of the comparator. Independent raters assessed effect sizes, study quality, and allegiance. A systematic literature search used the following criteria: randomized controlled trial of manual-guided psychodynamic therapy in adults, testing psychodynamic therapy against a treatment with efficacy established for the disorder under study, and applying reliable and valid outcome measures. The primary outcome was "target symptoms" (e.g., depressive symptoms in depressive disorders).
Results: Twenty-three randomized controlled trials with 2,751 patients were included. The mean study quality was good as demonstrated by reliable rating methods. Statistical analyses showed equivalence of psychodynamic therapy to comparison conditions for target symptoms at posttreatment (g=-0.153, 90% equivalence CI=-0.227 to -0.079) and at follow-up (g=-0.049, 90% equivalence CI=-0.137 to -0.038) because both CIs were included in the equivalence interval (-0.25 to 0.25).
Conclusions: Results suggest equivalence of psychodynamic therapy to treatments established in efficacy. Further research should examine who benefits most from which treatment.
Keywords: Efficacy; Equivalence Testing; Meta-Analysis; Outcome Studies; Pharmacotherapy; Psychotherapy.