Table 3.

Judgment about each risk of bias item for the included studies

Study	Bias due to confounding	Bias in selection of patients	Bias in classification of interventions	Bias due to deviations from intended interventions	Bias due to missing data	Bias in measurement of outcomes	Bias in selection of the reported result	Overall bias
Huang et al.	Serious	Moderate	Low	Serious	NI	Serious	Moderate	Serious
Wang et al.	Serious	Critical	Low	Critical	Moderate	Serious	Low	Critical
Zhang et al.	Serious	Serious	Low	Critical	NI	Serious	Moderate	Serious
Zhu et al.	Serious	Moderate	Low	Serious	NI	Moderate	Moderate	Serious

NI, no information