Strengths and Limitations
Compared with available systematic reviews of primary care trials,14–16 our analysis included a much larger number of trials, which allowed us to build subgroups of treatments with broadly similar interventions and delivery modes. The findings were highly consistent across the 3 analyzed effectiveness outcomes. Yet important limitations must be taken into account when interpreting our findings. The number of trials and the number of patients per treatment group are small. For at least one of these groups (remote therapist-led CBT), the numbers are so small that the respective results are accompanied by large uncertainty. Even within treatment groups intervention details sometimes differed to a considerable extent. The conditions under treatment varied across studies (major depression, minor depression, dysthymia) and were diagnosed by different criteria. In one-half the studies, participants were recruited by screening primary care patients; in the other one-half, depressed patients were referred by their primary care physicians. Some included trials have to be considered pragmatic effectiveness trials with broad inclusion criteria and allowing for variability between therapists, whereas others are explanatory efficacy studies trying to provide a proof of principle for a clearly defined manual-based treatment procedure. The psychological intervention was provided by a trained member of the routine primary care team in 4 trials only.
The intensity of treatment in usual care groups and the level of usual care interventions in groups receiving psychological treatments varied, which can have a major impact on the effect estimates. Only one-third of the trials were considered to have a low risk of bias, and publication bias seems at least possible. The reporting of treatment discontinuation, dropout from the study, and loss to follow-up rarely provided sufficient detail to assess whether attrition was due to acceptability of the treatment or organizational problems. No study reported adverse events or adverse effects for psychological treatments (not even studies including a pharmacotherapy treatment group). As a result, we could not assess acceptability and feasibility of treatments to the extent planned in our protocol.17 In summary, given the limited number, rather low quality, and considerable heterogeneity of the available studies, the findings of our review have to be interpreted carefully.