Cuijpers, P., Cristea, I.A., Karyotaki, E., Reijnders, M., Huibers, M.J.J. (2016). How effective are cognitive behavior therapies for major depression and anxiety disorders? A meta-analytic update of the evidence. World Psychiatry, 15, 245-258.
You might think that an esoteric topic like study quality should not really be of interest or concern to clinicians – but it is an important topic with practice implications. In this meta analysis Pim Cuijpers and his research group updated the meta analytic evidence for the efficacy of cognitive behavioral therapy (CBT) for a variety of disorders (major depressive disorder [MDD], generalized anxiety disorder [GAD], panic disorder [PAD], and social anxiety disorder [SAD]). The important thing about meta analyses is that the method combines the effect sizes from all relevant studies into a single metric – an average effect size. These average effect sizes are much more reliable than findings from any one single study. In fact, whenever possible, clinical decision-making should be based on a meta analysis and systematic review and not on a single study. Meta analyses also allow one to give more weight to those studies that have larger sample sizes, and that employ better methodologies. Even more, meta analytic techniques allow one to adjust the averaged effect size by taking into account publication bias (i.e., an indication of the effects from studies that might have been completed but were never published, likely because they had unfavorable findings). Usually, average effect sizes are lower when they are adjusted for study quality and publication bias. Cuijpers and colleagues’ meta analyses found that the unadjusted average effects of CBT were large for each of the disorders (ranging from g = .75 to .88 [confidence intervals not reported]). However adjusting for publication bias reduced the effects to medium-sized for MDD (g = .65) and GAD (g = .59). Only 17.4% of the individual studies of CBT were considered to be of “high quality” (i.e., studies that use the best methodology to reduce bias, like random allocation, blinding, using all the available data, etc.). After adjusting for study quality, the effects of CBT for SAD (g = .61) and PAD (g = .76) were also reduced to medium-sized. Not surprisingly, the effects of CBT were largest when the treatment was compared to a wait-list no-treatment control group. The effects were small to moderate when CBT was compared to treatment as usual or to a placebo.
Even when adjusting for study quality and publication bias, the average effects of CBT were medium-sized for a variety of common disorders compared to control conditions. Unfortunately, the quality of the studies was not high for most trials, reducing the effect sizes and lowering our confidence in the efficacy of the treatment. Nevertheless, the findings of this meta analysis suggest that CBT will likely have moderate effects for the average patient with MDD, SAD, PAD, and GAD.