The third problem we aimed to examine was the influence of waiting list control groups on the effects of CBT. We found that the vast majority of studies for the three anxiety disorders used a waiting list control group (77.4% of the comparisons for GAD, 78.6% for PAD, and 83.3% for SAD). In MDD, the number of studies using care-as-usual and pill placebo control condi- tions was larger, but still 44.4% (28 out of 63) of the included studies used a waiting list control group. This means that much of the evidence on the effects of CBT is based on the use of waiting list control groups. As indicated earlier, improvements found in patients on waiting lists are lower than can be expected on the basis of spontaneous remission19,185. Waiting list is prob- ably a “nocebo”21, considerably overestimating the effects of psychological treatments. This was confirmed in our meta- analysis, in which we found for each of the disorders that studies with a waiting list control group resulted in significantly higher effect sizes than those with a care-as-usual or pill placebo con- trol group.