Table 2.

Assessment of methodological quality for randomized controlled trials

Study ID	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of Outcome assessment	Incomplete outcome data	Selective reporting	Other sources of bias	Risk of bias
Gu and Guo 2004 [38]	Unclear	Unclear	High	Unclear	Low	Unclear	Unclear	High
Zhao et al. 2004 [39]	Unclear	Unclear	High	Unclear	Low	Unclear	Low	High
Xia and Chen 2006 [40]	Unclear	Unclear	High	Unclear	Unclear	Unclear	Low	High
Ji 2006 [41]	Unclear	Unclear	High	Unclear	Low	Unclear	Unclear	High
Shan and Zhou 2006 [42]	Unclear	Unclear	High	Unclear	Low	Unclear	Low	High
Wang et al. 2007 [43]	Unclear	Unclear	High	Unclear	Low	Unclear	Low	High
Li and Zhao 2008 [44]	Unclear	Low	Low	Unclear	Unclear	Unclear	Unclear	Unclear
Gao 2008 [45]	Unclear	Unclear	High	Unclear	Low	Unclear	Low	High
Xu et al. 2010 [46]	Low	Unclear	High	Unclear	Low	Unclear	Low	High
Zeng et al. 2013 [47]	Unclear	Unclear	High	Unclear	Low	Unclear	Low	High

NOTE: Unclear: unclear risk of bias; Low: low risk of bias; High: high risk of bias