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. This cohort study evaluates the existence of language and indexing biases among Chinese-sponsored randomized clinical trials on drug interventions. Question Do language and indexing biases exist among Chinese-sponsored randomized clinical trials on drug interventions? Findings This cohort study included 891 eligible Chinese-sponsored randomized clinical trials identified from English- and Chinese-language clinical trial registries. Among 470 published trials as of August 2019, positive trial findings were more commonly published in English-language journals and indexed in English-language bibliographic databases than negative trial findings. Meaning These findings suggest that language and indexing biases may lead to distorted, more positive results of drug interventions when synthesizing evidence.