Do certain countries produce only positive results? A systematic review of controlled trials.

OBJECTIVE To determine whether clinical trials originating in certain countries always have positive results. DATA SOURCES Abstracts of trials from Medline (January 1966-June 1995). STUDY SELECTION Two separate studies were conducted. The first included trials in which the clinical outcome of a group of subjects receiving acupuncture was compared to that of a group receiving placebo, no treatment, or a nonacupuncture intervention. In the second study, randomized or controlled trials of interventions other than acupuncture that were published in China, Japan, Russia/USSR, or Taiwan were compared to those published in England. DATA EXTRACTION Blinded reviewers determined inclusion and outcome and separately classified each trial by country of origin. DATA SYNTHESIS In the study of acupuncture trials, 252 of 1085 abstracts met the inclusion criteria. Research conducted in certain countries was uniformly favorable to acupuncture; all trials originating in China, Japan, Hong Kong, and Taiwan were positive, as were 10 out of 11 of those published in Russia/USSR. In studies that examined interventions other than acupuncture, 405 of 1100 abstracts met the inclusion criteria. Of trials published in England, 75% gave the test treatment as superior to control. The results for China, Japan, Russia/USSR, and Taiwan were 99%, 89%, 97%, and 95%, respectively. No trial published in China or Russia/USSR found a test treatment to be ineffective. CONCLUSIONS Some countries publish unusually high proportions of positive results. Publication bias is a possible explanation. Researchers undertaking systematic reviews should consider carefully how to manage data from these countries.