The effects of cognitive behavioral therapy are not systematically falling: A revision of johnsen and friborg (2015)

In a meta-analysis, Johnsen and Friborg (2015) reported a significant negative relationship between publication year and the effect sizes (ESs) of cognitive-behavioral therapy (CBT) for depressive disorders, suggesting its effectiveness was falling. We identified a series of methodological and conceptual caveats and consequently redid the meta-analysis. We used the same inclusion criteria, but only included randomized controlled trials and searched for additional eligible trials. We computed both within-group and between-group ESs for the CBT arm for the Beck Depression Inventory (BDI) and the Hamilton Rating Scale for Depression (HRSD). We assessed risk of bias, sample size, type of control group, and the study's country of origin and conducted subgroup, single, and multiple meta-regression analyses including publication year and other moderators. We identified 30 additional eligible trials. Within-group ESs presented huge heterogeneity estimates (I2 around 90%). Year of publication was significant in some single meta-regression analyses on the BDI, but not significant in others, in most analyses on the HRSD, and in any of the analyses on between-group ESs. Multiple regression models indicated that either year was not significantly related or that both year and country were significantly related to outcomes, with a temporal trend present solely in US studies. Year of publication does not appear to be a reliable and independent moderator of the effectiveness of CBT for depression. The linear "fall" reported by Johnsen and Friborg (2015) is most likely a spurious finding.