Fig. 2

Assessment of risk of bias based on the evaluation domains listed in the Cochrane Handbook for Systematic Reviews of Interventions criteria: A Risk of bias graph. A plot of the distribution of review authors’ judgments across studies for each risk of bias item presented as percentages. Note: Each color represents a different level of bias: red for high risk, green for low risk and yellow for unclear risk of bias. B Risk of bias summary: a review of the authors’ judgments about each risk of bias domain for each included study. Note: Each symbol represents a different level of bias: (?) = unclear risk of bias, (+) = low risk of bias, (−) = high risk of bias. C Funnel plot of publication bias analysis for published studies. Note: The circles represent individual studies included in the meta-analysis