Table 4.

Methodological quality of analysed studies.

Author, year	Random sequence generation	Allocation concealment	Blinding	Incomplete outcome data	Selective reporting	Other bias
Chen, 2010 [15]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Chu, 2010 [16]	Low risk	Low risk	High risk	Unclear	Low risk	Unclear
Han, 2008 [17]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Huang et al., 2006 [18]	Low risk	Low risk	High risk	High risk	Low risk	Unclear
Li and Han, 2010 [19]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Li et al., 2007 [20]	Low risk	Unclear	High risk	Unclear	Unclear	Unclear
P. Y. Lu, 2005 [21]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
J. Lu, 2005 [22]	Low risk	Low risk	High risk	Low risk	Low risk	Unclear
Qiu, 2006 [23]	Low risk	Low risk	High risk	Low risk	Low risk	Unclear
Quan, 2003 [24]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Tian, 2009 [25]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Wang, 2005 [26]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Wang, 2004 [27]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Zhang, 2009 [28]	Low risk	Unclear	High risk	Low risk	Unclear	Unclear
Zhang, 2007 [29]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear
Zhang et al., 2006 [30]	Unclear	Unclear	High risk	Unclear	Unclear	Unclear