Table 2.

Methodological quality of included trials.

Study ID	A	B	C	D	E	F	G
Gao et al. 2013 [28]	−	−	+	−	+	?	?
Qu 2013 [29]	−	+	+	+	−	?	?
Wu and Li 2012 [30]	−	−	+	+	−	?	?

+ = high risk, ? = unclear, and − = low risk. A = random sequence generation (selection bias); B = allocation concealment (selection bias); C = blinding of participants and personnel (performance bias); D = blinding of outcome assessment (detection bias); E = incomplete outcome data (attrition bias); F = selective reporting (reporting bias); G = other bias.