Publication Bias in Editorial Decision Making

CONTEXT: Studies with positive results are more likely to be published than studies with negative results (publication bias). One reason this occurs is that authors are less likely to submit manuscripts reporting negative results to journals. There is no evidence that publication bias occurs once manuscripts have been submitted to a medical journal. We assessed whether submitted manuscripts that report results of controlled trials are more likely to be published if they report positive results. METHODS: Prospective cohort study of manuscripts submitted to JAMA from February 1996 through August 1999. We classified results as positive if there was a statistically significant difference (P<.05) reported for the primary outcome. Study characteristics and indicators for quality were also appraised. We included manuscripts that reported prospective studies in which participants were assigned to an intervention or comparison group and statistical tests compared differences between groups. RESULTS: Among 745 manuscripts, 133 (17.9%) were published: 78 (20.4%) of 383 with positive results, 51 (15.0%) of 341 with negative results, and 4 (19.0%) of 21 with unclear results. The crude relative risk for publication of studies with positive results compared with negative results was 1.36 (95% confidence interval [CI], 0.99-1.88). After being adjusted simultaneously for study characteristics and quality indicators, the odds ratio for publishing studies with positive results was 1.30 (95% CI, 0.87-1.96). CONCLUSIONS: Among submitted manuscripts, we did not find a statistically significant difference in publication rates between those with positive vs negative results.