Depressive disorders constitute a major health problem in today's world. According to the World Health Organization, in the year 2000 depressive disorders were the leading cause of disability around the world and the fourth leading contributor to the global burden of disease. It is estimated that by the year 2020 depression will comprise the world's second largest disease burden, second only to ischemic heart disease . Currently, more than 150 million people around the world are suffering from a depression . Consequently, there is a high need for effective treatment.
The efficacy of existing psychotherapies for depressive disorders was recently reviewed by Roth & Fonagy . They conclude that in general psychotherapy is an effective treatment of depression when compared to placebo. Cognitive Behavioral Therapy (CBT), Interpersonal Psychotherapy (IPT), Problem Solving Therapy (PST), couple therapy, bibliotherapy, and computer-aided therapy all have shown to be effective treatment methods, consistently efficacious in around 50–60% of cases. In contrast, there still is limited evidence base for brief dynamic therapy, although this form of treatment is widely applied in clinical practice. According to Roth & Fonagy, the results of the few available studies on brief dynamic therapy are flawed by methodological problems and a probable bias due to investigator alliance. The outcomes of good-quality trials, they conclude, suggest effectiveness equal to the psychotherapies mentioned above, but the conclusions that can be drawn about this treatment method are severely limited by the paucity of trials. This view is shared by the Cochrane reviewers of short-term psychodynamic therapies for common mental disorders . They find modest to moderate gains of brief dynamic therapy for a variety of patients, but also conclude that these findings should be interpreted with caution because of limited data. Due to the scarcity of studies, the authors cannot draw any conclusions about the efficacy for depressed patients specifically. The present study aims at contributing to the gap in knowledge on this subject by comparing Short Psychodynamic Supportive Psychotherapy (SPSP) and Cognitive Behavioral Therapy in the treatment of depressed outpatients.
Short Psychodynamic Supportive Psychotherapy [5, 6] was developed in the early 90's as a structured psychodynamically orientated treatment for depressed outpatients within JellinekMentrum Mental Health Care Amsterdam (JMHC). Since then the acceptability, feasibility, and efficacy of this treatment have been compared to pharmacotherapy and combined treatment (SPSP and pharmacotherapy) in four randomized clinical trials [7–10]. In these studies, treatment acceptability is conceptualized by the number of patients refusing treatment when allocated to it by study randomization. Feasibility is the number of patients who terminate treatment prematurely. Efficacy refers to the number of patients recovered from depressive symptoms according to an independent observer, the patient and the therapist.
De Maat et al.  performed a 'mega-analysis' on the data of the first three trials, in which the effects of SPSP, pharmacotherapy, and combined treatment were compared both in terms of symptom reduction and quality of life improvement. The results suggest that the combination of SPSP and pharmacotherapy is more efficacious than pharmacotherapy alone. Besides patients finding combined therapy more efficacious in reducing depressive symptoms, no difference in efficacy was found when comparing SPSP and combined therapy. SPSP and pharmacotherapy were found to be equally efficacious, except for some indications that patients and therapists favor SPSP with regard to symptom reduction. The results of the above-mentioned trials further indicate a better acceptability of SPSP compared to both pharmacotherapy and combined treatment [8, 10]; fewer patients refuse SPSP because there is no medication involved. With regard to the feasibility, no differences were found .
In sum, previous research suggests that, while the combination of SPSP and pharmacotherapy seems to work better than pharmacotherapy alone, the superiority of combined treatment to SPSP is less obvious. In addition, SPSP and pharmacotherapy seem to be equally efficacious. Furthermore, the trial results provide support for the acceptability and feasibility of SPSP as an alternative treatment for depressed outpatients. Although combined treatment appears to be more efficacious than SPSP alone, this form of treatment is less well accepted by patients because of the required medication. Therefore SPSP might be a treatment of first choice for a great deal of depressed outpatients.
As mentioned earlier, so far SPSP has been compared to either pharmacotherapy or combined treatment. However, the question remains how SPSP compares with another established form of psychotherapy. Therefore the present study seeks to compare the acceptability, feasibility, and efficacy of SPSP to CBT, which is an evidence-based psychotherapy for the treatment of depressive disorders . In addition, it is unclear whether there are specific groups of patients, who might benefit from one of these treatments in particular. This study aims to gain more insight into this issue as well.
The aim of this study is twofold. First, the research compares Short Psychodynamic Supportive Psychotherapy and Cognitive Behavioral Therapy in terms of acceptability, feasibility, and efficacy. Second, it seeks to identify clinical predictors that distinguish patients that can benefit from either of these treatments in particular. These clinical predictors include demographic variables, (comorbid) psychiatric symptoms, cognitive and psychological patient characteristics, and the quality of the therapeutic alliance.
Considering the first research aim, it is hypothesized that both treatments will be equally efficacious. This is based on Roth and Fonagy's  conclusions described above. In line with the earlier trials, it is further hypothesized that both psychotherapies will be equally acceptable and feasible to patients as well, since neither includes the use of medication.
With regard to the second aim, it is expected that a predictive relationship will be found between patient characteristics and the efficacy of one of the two treatments in particular. Because systematic research on other predictive patient characteristics is relatively scarce, only three hypotheses are formulated. Though based on a small dataset, Van et al.  found that a subgroup of patients with comorbid symptoms of anxiety benefited less from SPSP. It is hypothesized that CBT will be more effective for this group of patients, because CBT is generally considered to be the treatment of choice for anxiety disorders. In addition, it is hypothesized that patients with comorbid personality disorders may benefit more from SPSP. While these patients are usually regarded as difficult to treat, SPSP showed positive treatment effects when combined with pharmacotherapy in a subgroup of depressed patients with comorbid personality pathology . Furthermore, it is thought that patients showing a higher degree of dysfunctional attitudes or cognitive reactivity to sad mood might respond better to CBT, because CBT specifically attends to these cognitive aspects.