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QUESTIONS: In patients with various clinical conditions, what is the clinical effect of placebo as a treatment for disease? Does the effect differ for subjective and objective outcomes?
Trials published before the end of 1998 were identified by searching Medline, EMBASE/Excerpta Medica, PsycLIT, Biological Abstracts, and the Cochrane Controlled Trials Register. Reference lists were reviewed and experts were contacted.
Studies were selected if patients were randomly allocated to a placebo group or an untreated group. Exclusion criteria were unconcealed randomisation, a sample of paid or healthy volunteers, non-blinding of assessors of objective outcomes, a > 50% dropout rate, or if the alleged placebo had a clinical effect not associated with the treatment ritual alone.
The primary outcome was that defined by the trial author or, if not defined, the most clinically relevant outcome.
114 trials were included. The typical …