Clinical outcomes by PIL categories. Anonymized studies are from (a) FD category, and (b) DD category, respectively. A test for subgroup differences indicates that studies from DD category report greater effects of real acupuncture compared to those from FD category. CI, confidence intervals; DD, deceptive disclosure of placebo acupuncture; FD, full disclosure of placebo acupuncture; PIL, participant information leaflet; SE, standard error; Std., standardized