Fig. 2

Risk of bias assessment for included studies. a Risk of Bias Graph. Literature quality was evaluated according to the following six points: ①generation of random distribution schemes; ②covert grouping; ③implementation of the blind method; ④Integrity of the data; ⑤non-selective reporting of results; ⑥other sources of bias. There are three bias assessment criteria “Low”, “High” and “Unclear” for each point, shown as the color green, yellow and red, respectively. b Risk of bias summary. The quality assessment of each literature has been shown. The color green, yellow and red represent low, high and unclear risk of bias, respectively