Assessment of Language and Indexing Biases Among Chinese-Sponsored Randomized Clinical Trials

IMPORTANCE: Language and indexing biases may exist among Chinese-sponsored randomized clinical trials (CS-RCTs). Such biases may threaten the validity of systematic reviews. OBJECTIVE: To evaluate the existence of language and indexing biases among CS-RCTs on drug interventions. DESIGN, SETTING, AND PARTICIPANTS: In this retrospective cohort study, eligible CS-RCTs were retrieved from trial registries, and bibliographic databases were searched to determine their publication status. Eligible CS-RCTs were for drug interventions conducted from January 1, 2008, to December 31, 2014. The search and analysis were conducted from March 1 to August 31, 2019. Primary trial registries were recognized by the World Health Organization and the Drug Clinical Trial Registry Platform sponsored by the China Food and Drug Administration. EXPOSURES: Individual CS-RCTs with positive vs negative results (positive vs negative CS-RCTs). MAIN OUTCOMES AND MEASURES: For assessing language bias, the main outcome was the language of the journal in which CS-RCTs were published (English vs Chinese). For indexing bias, the main outcome was the language of the bibliographic database where the CS-RCTs were indexed (English vs Chinese). RESULTS: The search identified 891 eligible CS-RCTs. Four hundred seventy CS-RCTs were published by August 31, 2019, of which 368 (78.3%) were published in English. Among CS-RCTs registered in the Chinese Clinical Trial Registry (ChiCTR), positive CS-RCTs were 3.92 (95% CI, 2.20-7.00) times more likely to be published in English than negative CS-RCTs; among CS-RCTs in English-language registries, positive CS-RCTs were 3.22 (95% CI, 1.34-7.78) times more likely to be published in English than negative CS-RCTs. These findings suggest the existence of language bias. Among CS-RCTs registered in ChiCTR, positive CS-RCTs were 2.89 (95% CI, 1.55-5.40) times more likely to be indexed in English bibliographic databases than negative CS-RCTs; among CS-RCTs in English-language registries, positive CS-RCTs were 2.19 (95% CI, 0.82-5.82) times more likely to be indexed in English bibliographic databases than negative CS-RCTs. These findings support the existence of indexing bias. CONCLUSIONS AND RELEVANCE: This study suggests the existence of language and indexing biases among registered CS-RCTs on drug interventions. These biases may distort evidence synthesis toward more positive results of drug interventions.