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The logic of the randomized double-blind placebo control group design is presented, and problems with using the design in psychotherapy are discussed. Placebo effects are estimated by examining clinical trials in medicine and psychotherapy. In medicine, a recent meta-analysis of clinical trials with treatment, placebo, and no treatment arms was conducted (Hróbjartsson & Gøtzsche, 2001), and it was concluded that placebos have small or no effects. A re-analysis of those studies, presented here, shows that when disorders are amenable to placebos and the design is adequate to detect the effects, the placebo effect is robust and approaches the treatment effect. For psychological disorders, particularly depression, it has been shown that pill placebos are nearly as effective as active medications whereas psychotherapies are more effective than psychological placebos. However, it is shown that when properly designed, psychological placebos are as effective as accepted psychotherapies.
Wampold et al. (Sat,) studied this question.