Cognitive-behavioral therapy (CBT) is widely researched and recommended as an evidence-based treatment for adult depression, but despite the strength of research comparing CBT approaches with other forms of care, there are few recent systematic reviews on this topic.

Cuijpers and collaborators provide such a review in a recent meta-analysis published in The Canadian Journal of Psychiatry, where they examine the efficacy of CBT for adult depression, both alone and in combination with other treatments.

Methods

The authors included randomised clinical trials in adults, comparing CBT with a control intervention (wait-list, treatment as usual, placebo or other) or with another form of treatment (psychotherapy or  medication). Studies were included if the primary clinical problem being treated was depression, evaluated either by a diagnostic interview or by self-report scales. Studies comparing the combination of CBT and pharmacotherapy with pharmacotherapy alone were also included.

Two independent raters evaluated included studies for methodological quality, using four criteria from the risk of bias assessment tool developed by the Cochrane Collaboration:

1. Adequate sequence generation
2. Allocation concealment
3. Blinding of outcome assessors
4. Incomplete outcome data

Effect sizes (ES) were calculated for each comparison between CBT and another group at post-test (standardised mean difference) and then transformed into Hedges’ g in order to adjust for bias due to small size (.20, .50 and .80 correspond to small, moderate and respectively large ES). The standardised mean difference was also transformed in an index more amenable to clinical interpretation, the NNT, indicating the number of patients that have to be treated to generate one additional positive outcome.

Results

115 studies met the inclusion criteria and were included in the meta-analysis.

• CBT vs control (wait-list, treatment as usual, placebo or other):
  • The mean ES (g) was 0.71 (95% CI 0.62 to 0.79)
  • Corresponding to a NNT of 2.60

However, it is important to note that the authors evidenced considerable publication bias (confirmed by three methods), and also that study quality was a significant moderator of the results, with ES decreasing with the increase of study quality (a decrease of .14  with each of the quality criteria that was not met).

Additionally, effect sizes were smaller in clinical samples in studies conducted in the United States (as opposed to other countries), and in comparison with placebo and (or) other control groups, different than treatment as usual or waitlist.

• CBT plus pharmacotherapy vs pharmacotherapy:
  • The mean ES (g) was 0.49 (95% CI 0.29 to 0.69)
  • Corresponding to an NNT of 3.68
• CBT vs pharmacotherapy:
  • The mean ES (g) was 0.03 (95% CI –0.13 to 0.18, P > 0.05)
  • Indicating no significant overall difference in outcomes
• CBT vs other psychotherapies:
  • The ESs ranged from -0.02 to 0.25 and were all non-significant
  • But for some of the alternative forms of therapy considered, there were only a small number of RCTs comparing them with CBT

Conclusions

The authors conclude that:

Based on a large number of comparisons of CBT with a control or alternate intervention group, our meta-analysis found that CBT is an efficacious treatment for adult depression.

However they also add:

This effect size is an overestimation of the true ES, because we also found clear indications for publication bias. Further, the inclusion of a considerable number of lower quality studies has probably also led to an overestimation of the mean ES.

Other important conclusions:

• The combination of CBT and pharmacotherapy was superior to pharmacotherapy alone for the treatment of adult depression
• However, in contrast to previous meta-analysis, Cuijpers et al found no difference in efficacy between CBT and pharmacotherapy
• Comparisons with other forms of psychotherapy indicate CBT is no less and no more efficient, but for some of these forms of psychotherapy there are only a few studies comparing them with CBT

Limitations

• The methodological quality of many of the studies included in the meta-analysis was subpar, with only  37% (43/115) of the studies meeting at least 3 of the 4 quality criteria
• Although the number of included studies was substantial, some of the subgroup contrasts were based on a small number of studies, which may have contributed to the failure to show significant differences between subgroups of studies
• The meta-analysis only examined the short-term outcomes of CBT

Link

Cuijpers, P., Berking, M., Andersson, G., Quigley, L., Kleiboer, A., Dobson, K.S., 2013. A meta-analysis of cognitive-behavioural therapy for adult depression, alone and in comparison with other treatments. Can J Psychiatry 58, 376–385. [PubMed abstract]