Table 2.

Quality assessment of risk of bias in included studies

References	Random sequence generation	Allocation concealment	Blinding	Incomplete outcome data	Free of selective reporting	Free of other bias
Kiely et al. (2001) [16]	Yes	Yes	Unclear	Yes	Yes	Unclear
Pornrattanamaneewong et al. (2012) [22]	Yes	Yes	Unclear	Yes	Yes	Unclear
Shen et al. (2005) [29]	No	Yes	Unclear	Yes	Yes	Unclear
Eum et al. (2006) [8]	Unclear	Unclear	Unclear	Yes	Yes	Unclear
Roy et al. (2006) [26]	Yes	Unclear	Unclear	Yes	Yes	Unclear
Raleigh et al. (2007) [24]	Yes	Unclear	Unclear	Yes	Yes	Unclear
Stucinskas et al. (2009) [30]	Yes	Yes	Unclear	Yes	Yes	Unclear
Madadi et al. (2010) [19]	Yes	Yes	Yes	Yes	Yes	Unclear
Chareancholvanich et al. (2012) [4]	Yes	Yes	Unclear	Yes	Yes	No

‘Yes’ indicates low risk of bias, ‘Unclear’ indicates unclear risk of bias, ‘No’ indicates high risk of bias