Another limitation is that apart from studies examining PTSD, sam- ples were not particularly diverse racially. The mean sample of non- PTSD studies was 82% white, with only two non-PTSD studies using a sample with more than 23% non-whites. Future research is needed to examine the generaliz ability of the present results to more diverse samples. Finally, it should be noted that there was some degree of heterogeneity in the types of placebo conditions used across studies. Although no difference between studies using psychological versus pill placebo was found for either controlled or pre–post placebo effect sizes, the lack of complete uniformity in control conditions limits the precision of the comparison. For instance, studies using pill placebo typically do not control the time spent with a clinician and may attract a unique sample that is open to both pharmacological and psychother- apy treatments. In studies using psychological placebos, on the other hand, providers and even patients may know that they are assigned to a control condition. In addition, there was some variability in the form and content of psychological placebo treatments across studies, and it is possible that this affected the relative effects of CBT seen in differ- entstudies.While not considered atrue placebo condition for the pur- posesofthisstudy,futureresearchwouldalsobenefitfromcomparing fulltreatmenttominimallyinstructedself-guidedCBT.