Evidence-based treatments for depression include pharmacological and psychological interventions. Within psychological interventions, cognitive behavioral therapy (CBT) is one of the most extensively researched evidence-based approaches for depression (Cuijpers, 2015). However, even if optimal treatment and access to services were available to all patients, the burden of depression would be reduced by only 30% (Andrews et al., 2004). Moreover, as depression represents the disorder with the highest drop-out rates during CBT treatment (36.4%) (Fernandez et al., 2015), and a relapse rate of 54% for treatment responders within the two years after treatment termination (Vittengl et al., 2007), it is pivotal to improve treatment for depression. It has been argued that this is less a question of developing novel psychological treatments as of determining how existing treatments may be improved (Cuijpers, 2015) and better disseminated to increase retention rates and to use the waiting phase to rise interest in therapy (Fernandez et al., 2015). Due to hopelessness and the discouraging character of the disorder, this poses a particular challenge.

To meet this aim, Metacognitive Training for Depression (D-MCT) has been developed as a low-threshold, highly standardized and yet easy to administer group concept for the treatment of depression. It is conceptualized as a variant of CBT that adopts a metacognitive perspective focusing on the modification of cognitive biases, and is compatible with a general CBT treatment approach. Use of standardized presentations reduces time needed for preparation and administration of the training; moreover, this "packaging" increases the accessibility of D-MCT to a wide range of health care providers, and encourages standardization across therapists. The training seeks to enable group members to recognize and correct the often automatic and unconscious thought patterns that accompany depression. To this end, it attempts to challenge cognitive biases through the use of creative and engaging exercises supported by a multimedia presentation (e.g., insight based on "aha" effects rather than psychoeducation) and to encourage patients to take a metacognitive perspective ("think about one's thinking"). The training is highly flexible with regard to depth and intensity. Patients do not need to (but may) discuss their own problems, and can still experience how cognitive biases work and influence one's mood in a playful atmosphere. The training is conceptualized as an open group: New patients can join the group in every session. Thus, the threshold for administration of and participation in this intervention is low.

The general structure of and exercises in D-MCT were inspired by Metacognitive Training for psychosis (Moritz et al., 2014); however, contents were modified upon to suit the specific problems of individuals with depression. Beside depressive thought patterns already targeted in CBT (e.g., overgeneralization, "mind reading"), a number of general cognitive biases, which have been identified by basic cognitive research, form the core of D-MCT (e.g., mood-congruent memory (Mathews and MacLeod, 2005)). Finally, as in Metacognitive Therapy (MCT) sensu Adrian Wells (Wells, 2011) dysfunctional coping strategies (i.e., thought suppression, rumination as problem-solving) are challenged. D-MCT thus blends established elements from CBT and MCT as well as newly developed and evidence-based exercises in one coherent metacognitive approach.

D-MCT was positively evaluated with regard to feasibility and acceptance in a non-randomized pilot study (Jelinek et al., 2013). Moreover, efficacy of D-MCT was suggested in a randomized controlled trail (RCT) in comparison to an active control intervention (Jelinek et al., 2016). In this trial patients with depressive disorder were completing a psychosomatic outpatient treatment program and were randomly assigned to either D-MCT or general health training. Severity of depression and cognitive biases were assessed at baseline (t0), post treatment (t1) and 6 months (t2) later by raters blind to diagnostic status. Intention-to-treat analyses demonstrated that at the end of treatment, as well as 6 months later, improvement in depression was significantly greater in the D-MCT relative to the health training group at medium effect sizes. A significantly greater number of patients in the D-MCT group were in remission at 6-month follow-up. Moreover, the decrease in cognitive biases and increase in psychological well-being/quality of life was larger in the D-MCT than the health training group over time. Patients' subjective appraisal of D-MCT was also positive (Jelinek et al., 2017).

Aim of the current study is to investigate the acceptance and efficacy of D-MCT in outpatients.The Hamilton Depression Rating Scale (HDRS, 17-item version) total score as well as the Quick Inventory of Depressive Symptomatology (QIDS) serve as primary outcome. Self-assessed depression, dysfunctional beliefs, self-esteem, quality of life, rumination, remission rate as well as neuropsychological functioning serve as secondary outcomes.