Figure 2.

Assessment of risk of bias in this meta-analysis. Risk of bias summary. (A) Summary of risk of bias for each trial assessed by Cochrane Collaboration’ tool, plus sign was for a judgment of Yes or low risk of bias, minus sign was for a judgment of No or high risk of bias, and question mark was for a judgment of Unclear, or uncertain risk of bias, which meant there was insufficient information to permit a judgment of Yes or No. Risk of bias graph. (B) Risk of bias graph about each risk of bias item presented as percentages across all included studies.