Table 2.

Methodological quality assessment of randomized controlled trials: the Cochrane collaboration’s tool for assessing risk of bias^*

Study (year)	Selection bias	Performance bias	Detection bias	Attrition bias	Reporting bias	Other bias
An et al. (2018)	Low risk	Low risk	Low risk	Low risk	Low risk	Unclear
Zhang et al. (2017)	Low risk	Low risk	Low risk	Low risk	Low risk	Unclear
An et al. (2017)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear
Zhou et al. (2016)	Low risk	Low risk	Low risk	Low risk	Low risk	Unclear
Liu et al. (2016)	Low risk	Low risk	Low risk	Low risk	Low risk	Unclear
He et al. (2016)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear
Guo et al. (2015)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear
Liu et al. (2018)	Low risk	Low risk	Low risk	Low risk	Low risk	Unclear
Shu et al. (2014)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear
Hu et al. (2013)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear
Tao et al. (2016)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear
Huang et al. (2015)	Low risk	Low risk	Low risk	Low risk	Low risk	Unclear
Yan et al. (2016)	Unclear	Low risk	Low risk	Low risk	Low risk	Unclear

^*Results of the articles were divided into low risk, unclear risk, and high risk.