Background: Previous meta-epidemiological studies based on Western medicine have found several trial characteristics influencing the effect estimates of randomized controlled trials (RCTs). However, whether there were similar associations in Chinese herbal medicine RCTs is unclear. Furthermore, the characteristics specific to Chinese medicine have not been investigated.
Objectives: This meta-epidemiological study aimed to explore potential trial characteristics associated with treatment effect estimates in Chinese herbal medicine RCTs, including both Chinese medicine–specific characteristics and characteristics common to Chinese and Western medicine.
Methods: Three English databases and two Chinese databases were searched for systematic reviews on Chinese herbal medicine treatment published from January 2011 to July 2021. The difference in effect estimates was presented as the ratio of odds ratio (ROR) for binary outcomes and the difference in standardized mean differences (dSMD) for continuous outcomes. The two-step method was used for meta-epidemiological analyses.
Results: We included 91 systematic reviews, comprising 1,338 RCTs. For binary outcomes, RCTs with syndrome differentiation (ROR: 1.23, 95% CI: 1.07, 1.39), adopting Chinese medicine formula (ROR: 1.19, 95% CI: 1.03, 1.34), of low risk of bias in incomplete outcome data (ROR: 1.29, 95% CI: 1.06, 1.52) and selective outcome reporting (ROR: 1.12, 95% CI: 1.01, 1.24), and having sample size ≥100 (ROR: 1.23, 95% CI: 1.04, 1.42) tended to have greater effect estimates. For continuous outcomes, RCTs based on Chinese medicine diagnostic criteria (dSMD: 0.23, 95% CI: 0.06, 0.41), judged as high/unclear risk of bias on allocation concealment (dSMD: -0.70, 95% CI: -0.99, -0.42), rated as low risk of bias for incomplete outcome data (dSMD: 0.30, 95% CI: 0.18, 0.43), being single-center (dSMD: -0.33, 95% CI: -0.61, -0.05), not using intention-to-treat data analysis (dSMD: -0.75, 95% CI: -1.43, -0.07), and without funding support (dSMD: -0.22, 95% CI: -0.41, -0.02) showed larger effect estimates.
Conclusions: Our findings will provide empirical evidence for developing a critical appraisal tool specific to assessing risk of bias of Chinese herbal medicine RCTs.
Patient, public and/or healthcare consumer involvement: No patient or member of the public was involved in conducting this study.