Cognitive behavior therapy for anxiety disorders: 40 years of progress

Cognitive-behavior therapies (CBT) have been evaluated in randomized controlled studies (RCT) and anxiety disorders since 1966 and for each disorder there are at least two CBT methods that are considered evidence based (empirically supported) today. Numerous meta-analyses have evaluated the efficacy of these methods against various control conditions. However, none has looked at whether modern CBT studies lead to better treatment effects than were obtained 10-40 years ago. The aim of this paper is to present a meta-analysis focusing on the mean extent of change achieved by the CBT treatments across decades (from the 1970s onwards). Database searches yielded a total of 432 RCTs for the anxiety disorders combined and 364 of these allowed calculation of within-group effect size (ES) or percentage clinical improvement. Separate ESs were calculated for three central measures: independent assessor rating, self-report and behavioral approach test. The results showed that in most instances there was no significant change in ES across time. In a few instances, the treatment effects were greater in modern studies. However, it was more common with a negative development, or a mixed development (first positive then negative or vice versa). There was no significant change in proportion of clinical improvement. Treatment time and attrition either increased or remained stable. If the single studies that gave the highest ES each decade were compared, all anxiety disorders besides panic disorder and obsessive-compulsive disorder showed a positive development. Possible explanations to the results are discussed.