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

Abstract

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.