Table 2.

The Jadad score for assessing risk of bias.

Study (first author, year)	Random sequence generation	Double blinding	Withdrawals and dropouts	Jadad score
Zhang, 2006 [31]	2	0	0	2
Chen, 2010 [32]	2	1	1	4
Yang and Liu, 2010 [33]	2	0	1	3
Lin, 2010 [34]	2	1	0	3
Peng et al., 2010 [35]	2	0	1	3
Wan, 2010 [36]	2	1	1	4
Liu et al., 2011 [37]	2	0	0	2
Wang, 2013 [38]	2	0	1	3
Wu et al., 2014 [39]	2	2	1	5
Liao, 2018 [40]	2	0	0	2