What Works for Whom and How? Mechanisms of Change in Psychotherapy

Background: Major depressive disorder (MDD) is a prevalent psychiatric condition associated with significant disability, mortality and economic burden. MDD is ranked fourth in terms of disease burden as defined by the World Health Organization (2001). Cognitive Behavioral Therapy (CBT) and Psychodynamic Psychotherapy (PDT) are found to be equally effective for patients with depression. However, many patients do not respond sufficiently to treatment and relapse rates are high. To be able to offer individualized treatment, a clinically important question is therefore whether some patients profit more from one of the two therapies. At present little is known on which patient characteristics (moderators) may be associated with differential outcomes of CBT and PDT and through what kind of therapeutic processes and mechanisms (mediators) improvements occur in each therapy mode. There are actually only theoretical assumptions sparsely supported by research findings on what moderates and mediates the treatment effects of CBT and PDT.

Aims: The overall aim of this project is to examine putative moderators and mediators in CBT and PDT and develop more basic knowledge about their impact on outcomes of psychotherapy for patients with MDD.

Methods and study design: The study is a randomized clinical trial. One hundred patients will be randomized to one of two treatment conditions. The patients will be treated over 28 weeks with either CBT (one weekly session over 16 weeks and 3 booster sessions (monthly) during the rest of the 28 week study period) or PDT (one weekly session in 28 weeks). The patients will be evaluated at baseline, during therapy, at the end of therapy, and at follow-up investigations 1 and 3 years after treatment termination. The outcome measures comprise a large range of clinical and process variables, including assessment tools measuring specific preselected putative moderators and mediators.

Discussion: The clinical outcome of this trial may guide clinicians to decide what kind of treatment should be offered the individual patient. Moreover, it will shed light on what kind of mechanisms in psychotherapy that is followed by symptom improvement and increased psychosocial functioning.