2.6 Quality assessment
Risk of bias was used the Cochrane Collaboration’s risk of bias assessment tool [13]. Two authors (J Jiang and YP Huang) independently rated each study as “high”, “low”, “unclear” for risk of bias assessment, W Zhang helped resolve when disagreements were reached. The evaluation tools mainly include the method of random allocation sequence, blinding of subjects or trial personnel, blinding of outcome assessors, completeness of outcome data, selective reporting, allocation concealment, and other sources of bias.