Assessment of risk of bias in included studies
Two authors (YX and HL) independently assessed the risk of bias for each included randomised trial. Disagreements were resolved by discussion with JL. We assessed the following domains (Schulz 1995; Moher 1998; Jüni 2001; Kjaergaard 2001; Wood 2008; Lundh 2012; Savovic 2012a; Savovic 2012b):