Table 2.

Risk of bias assessment in included studies 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
Teekachunhatean et al30	?	+	+	+	+	?	+	Unclear
Yu and Zhang39	?	?	−	?	+	?	+	High
Cao et al48	Random number table	?	−	?	?	?	+	High
Gu49	?	?	−	?	+	?	+	High
Yu50	?	?	−	?	+	?	+	High
Zhang and Sun51	?	?	−	?	?	?	+	High
Zhong and Zhong52	?	?	−	?	?	?	+	High
Dong53	?	?	−	?	+	?	+	High
Huang and et al54	?	?	−	?	+	?	+	High
Jiang55	?	?	−	?	?	?	+	High
Wang56	?	?	−	?	?	?	+	High
Zhou and Wang57	?	?	−	?	?	?	+	High

+, Low risk of bias; −, high risk of bias; ?, unclear risk of bias.