Quality assessment
The risk of bias of each study was conducted using the Risk of Bias table in Review Manager 5.4.1 to critically judge the information within each article and to evaluate whether each study involved in meta-analysis meets the internal validity criteria. Standard criteria including sequence generation (selection bias), allocation concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data (attrition bias), selective reporting (reporting bias) were used to assess the quality of each study. The risk of bias was classified into low, unclear, or high with explanations given for each criterion. Publication bias was also accessed using funnel plots.