Quality assessment and publication bias
We assessed the quality of the included trials based on the information in the Methods section and supplementary materials about them. The quality of the RCTs was assessed using the Cochrane Collaboration’s risk-of-bias tool for randomized trials (RoB) (11), which consists of six domains and allowance for any other bias, with risk-of-bias judgements for RCTs ranging from ”high,” ”unclear” to ”low.” We assessed observational studies using the Newcastle-Ottawa Scale (12) with scores ranging from 0 to 9 points (a higher score indicated less bias). Two authors independently assessed the studies’ quality and resolved disagreements through consensus.
We used funnel plots to assess publication bias, which were calculated using RevMan 5.3 software. The Egger regression test was used to measure funnel plot asymmetry, and was calculated using Stata 12.0 (StataCorp LP, College Station TX, USA).