Table 3.

Risk of bias assessment based on the Cochrane handbook.

Included studies	Random sequence generation	Concealment of allocation	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Other bias	Risk of bias
Song et al., 2009 [30]	?	?	—	?	+	?	+	High
Hu, 2011 [31]	?	?	—	?	?	?	+	High
Sun et al., 2012 [32]	?	?	—	?	?	?	+	High
Li, 2013 [33]	?	?	—	?	?	?	?	High
Zhang, 2016 [34]	?	?	—	?	?	?	+	High
Shen, 2016 [35]	+	?	—	?	?	?	+	High

+: low risk of bias; —: high risk of bias; ?: unclear risk of bias.