Table 2.

Risk of bias.

Studies	Sequence generation	Allocation concealment	Investigator blinding	Patients blinding	Incomplete outcomes data	Selective outcome reporting	Other source of bias	Overall risk of bias
Zhao, 200424	Low	Low	Unclear	Low	Low	Low	Low	Low
Hu, 200619	Low	Low	Unclear	Low	Low	Low	Low	Low
Li, 200920	Low	Low	Low	Low	Low	Low	Low	Low
Lu, 20088	Low	Low	Low	Low	Low	Low	Low	Low
Zhao, 200323	Low	Low	Unclear	Unclear	Low	Low	Low	Low
Ye, 200722	Low	Low	Low	Low	Low	Low	Low	Low
Li, 201021	Low	Low	Low	Low	Low	Low	Low	Low