Citation bias of hepato-biliary randomized clinical trials

The objective of this study was to assess whether trials with a positive (i.e., statistically significant) outcome are cited more often than negative trials. We reviewed 530 randomized clinical trials on hepato-biliary diseases published in 11 English-language journals indexed in MEDLINE from 1985-1996. From each trial, we extracted the statistical significance of the primary study outcome (positive or negative), the disease area, and methodological quality (randomization and double blinding). The number of citations during two calendar years after publication was obtained from Science Citation Index. There was a significant positive association between a statistically significant study outcome and the citation frequency (beta, 0.55, 95% confidence interval, 0.39-0.72). The disease area and adequate generation of the allocation sequence were also significant predictors of the citation frequency. We concluded that positive trials are cited significantly more often than negative trials. The association was not explained by disease area or methodological quality.