Fig. 2

Proportion of studies meeting each quality score criterion. Results of the risk of bias of the 39 studies involved in the systematic review were shown by bar charts. For the items 1 to 10, “Yes” means that the description of measurements meets the item requirements, indicating low risk of bias, “No” means that the description does not meet the item requirements, indicating high risk of bias, and “Unclear” means there is no relevant reports, indicating unclear risk of bias. With the item 11 and 12, “Yes” indicated reported and “No” indicated unreported