Assessment of duplicate publication of Chinese-sponsored randomized clinical trials

IMPORTANCE Duplicate publications of randomized clinical trials are prevalent in the health-related literature. To date, few studies have assessed the interaction between duplicate publication and the language of the original publication. OBJECTIVE To assess the existence of duplicate publication and the extent to which duplicate publication is associated with the language of the original publication. DESIGN, SETTING, AND PARTICIPANTS In this retrospective cohort study, eligible randomized clinical trials were retrieved from trial registries, and bibliographic databases were searched to determine their publication status. Eligible randomized clinical trials were for drug interventions from January 1, 2008, to December 31, 2014. The search and analysis were conducted from March 1 to August 31, 2019. The trial registries were either primary registries recognized by the World Health Organization or the Drug Clinical Trial Registry Platform sponsored by the China Food and Drug Administration. EXPOSURES Individual randomized clinical trials with positive vs negative results. MAIN OUTCOMES AND MEASURES Journal articles were classified as main articles (determined by largest sample size and longest follow-up among all journal articles derived from that randomized clinical trial) and duplicates. The duplicates were classified into 4 types: (1) unreferenced subgroup analysis (article did not disclose itself as a subgroup analysis or reference its main article); (2) unreferenced republication (article did not disclose itself as a replicate of the main article or reference it); (3) unreferenced interim analysis (article did not disclose itself as an interim analysis or reference its main article); and (4) partial duplicate (article did not disclose its sharing a subset of participants with other articles or reference them). RESULTS Among 470 randomized clinical trials published by August 2019 as journal articles, 55 (11.7%) had 75 duplicates, of which 53 (70.7%) were cross-language duplicates. Of the 75 duplicates, 33 (44.0%) were unreferenced republications, 25 (33.3%) unreferenced subgroup analyses, 15 (20.0%) unreferenced interim analyses, and 2 (2.7%) partial duplicates. When the main article of a randomized clinical trial was published in Chinese, those with positive findings were 2.48 (95% CI, 1.08-5.71) times more likely to have subsequent duplicate publication than those with negative findings. CONCLUSIONS AND RELEVANCE In this study, most duplicates were cross-language duplicates and the most common type was unreferenced republication of the main article. Duplicate publication bias exists when the main articles of randomized clinical trials were published in Chinese, potentially misleading readers and compromising journals and evidence synthesis.