RESULTS
Study Selection, Characteristics of Included Studies, and Risk of Bias
A total of 30 studies (reported in 37 publications) met the inclusion criteria (Table 1; see Supplemental Appendix for a flowchart providing details about the selection process and the full reference lists of included trials). Thirteen trials recruited patients who were referred from the primary care physician, 14 used a screening procedure, and 3 used mixed approaches. Ten trials exclusively included patients meeting diagnostic criteria for major depression; and in 14 trials depression was either not formally diagnosed according to standardized schemes, or patients with a variety of depressive disorders were included. Six trials included only patients with minor depression, dysthymia, or either minor depression or dysthymia. Inclusion criteria were liberal in most trials, making it likely that study participants represent primary care patients with the respective depressive disorders fairly well. The 30 trials included a total of 32 groups receiving a psychological intervention. Twenty-seven trials had a usual care group for control, while 3 trials (with an additional group treated with pharmacotherapy) had a placebo control group. Furthermore, 6 trials with a usual care control group had additional comparator groups that were not included in our analyses (2 pharmacotherapy trials, 1 acupuncture, 1 talking control, 1 a psychoeducational depression recurrence prevention program, and 1 a relaxation control). The total number of patients randomized into the 62 treatment arms included in our analyses was 5,159 (median = 152, range = 29–453).
The psychological intervention was face-to-face CBT in 7 treatment groups, face-to-face problem-solving therapy in 4, face-to-face interpersonal psychotherapy in 2, other face-to-face psychological interventions in 6 (5 variable counseling interventions and 1 psychoeducational intervention), remote therapist-led CBT in 3, remote therapist-led problem-solving therapy in 2, guided self-help CBT in 4, and no or minimal contact CBT in 4 treatment groups. There were no trials investigating psychodynamic therapy or face-to-face treatments in a group setting. Five of the 6 trials in patients with minor depression and/or dysthymia investigated face-to-face (N = 3) or therapist-led (N = 2) problem-solving therapy. In trials limited to patients with major depression, the psychological treatment was provided more frequently as a face-to-face intervention.
The overall risk of bias was considered low in 10, unclear in 9, and high in 11 trials (Table 1). The reporting of intervention details in usual care groups and of cointerventions (eg, percentage of patients receiving antidepressants) in the groups receiving psychological treatment was often insufficient; therefore, we were not able to classify this aspect in a reliable manner. From what was reported, however, it is obvious that the level of intervention or cointervention varied considerably.