Table 2. Risk of bias of included studies.
| Reference (author, year and country) | A | B | C | D | E | F | G | H |
|---|---|---|---|---|---|---|---|---|
| Ntritsou et al. 2014 USA18 | + | + | + | − | + | + | ? | + |
| Chu et al. 2012 Hong Kong19 | + | + | + | − | + | + | ? | + |
| Wang et al. 2010 Denmark20 | + | + | + | − | + | + | ? | + |
| Zyloney et al. 2010 USA21 | + | − | + | − | + | ? | ? | + |
| Jubb et al. 2008 UK22 | + | − | + | − | + | + | ? | + |
| Chung et al. 2012 Hong Kong23 | + | + | + | − | + | − | ? | + |
| Barlas et al. 2006 UK24 | + | − | + | − | + | ? | ? | + |
| Wayne et al. 2005 US25 | + | + | + | − | + | + | ? | + |
| Sahin et al. 2010 Turkey26 | + | + | + | − | + | + | ? | + |
| Fanti et al. 2003 Italy27 | + | − | + | − | + | + | ? | + |
| Hsing et al. 2012 Brazil28 | + | − | + | − | + | + | ? | + |
| Gosman-Hedström et al. 1998 Sweden29 | + | + | + | − | + | + | ? | + |
| Jing et al. 2009 China30 | + | + | + | − | + | + | ? | + |
| Kong et al. 2009 USA31 | + | − | + | − | + | ? | ? | + |
| Darbandi et al. 2013 Iran32 | + | ? | + | − | + | ? | ? | + |
| Yang et al. 2012 China33 | + | ? | + | − | + | + | ? | + |
| Liu et al. 2013 China34 | + | + | + | − | + | + | ? | + |
| Zhang et al. 2014 China35 | + | + | + | − | + | + | ? | + |
| Mao et al.2014 USA36 | + | + | + | − | + | + | + | + |
| Leung et al. 2011 Hong Kong37 | + | + | + | − | + | + | ? | + |
| Rusy et al. 2002 USA38 | + | ? | + | − | + | + | ? | + |
| Yang et al. 2014 China39 | + | ? | + | − | + | + | + | + |
| Chen et al. 2013 China40 | + | ? | + | − | + | + | ? | + |
| Quispe-Cabanillas et al. 2012 Brazil41 | + | ? | + | − | + | + | + | + |
| Aranha et al. 2015 Brazil42 | + | ? | + | − | + | − | + | + |
| Yu et al. 2013 Hong Kong43 | + | + | + | ? | + | + | ? | + |
| Li et al. 2010 China44 | + | + | + | − | + | + | + | + |
| Zheng et al. 2007 Australia45 | + | + | + | − | + | − | ? | + |
| Li et al. 2013 China46 | + | ? | + | ? | + | + | ? | + |
| Lin et al. 2002 Taiwan47 | + | ? | + | ? | + | + | ? | + |
| Chen et al. 2013 Taiwan48 | + | ? | + | − | + | − | ? | + |
| Schukro et al. 2014 Austria49 | + | ? | + | ? | + | + | ? | + |
| Yu et al. 2014 China50 | + | ? | + | − | + | + | ? | + |
| Xie et al. 2014 China51 | + | ? | + | ? | + | + | ? | + |
| Sim et al. 2002 Singapore52 | + | ? | + | − | + | + | ? | + |
| Song et al. 2009 China53 | + | ? | + | ? | + | ? | ? | + |
| Shafshak 1995 Egypt54 | + | ? | + | ? | ? | ? | ? | + |
| Franasiak et al. 2012 USA55 | + | + | + | − | + | + | ? | + |
| Naslund et al. 2002 Sweden56 | + | ? | + | − | + | ? | ? | + |
| Shen et al. 2000 US57 | + | + | + | − | + | + | ? | − |
| Wyon et al. 2004 Sweden58 | + | + | + | − | + | + | ? | − |
| Zhang et al. 2012 Hong Kong59 | + | ? | + | − | + | + | + | − |
| Zheng et al. 2010 Australia60 | + | + | + | − | + | + | ? | + |
| Ma et al. 2010 China61 | + | + | + | − | + | + | ? | + |
| Wang et al. 2014 Taiwan62 | + | ? | + | − | + | + | ? | + |
| Yeung et al. 2011 Hong Kong63 | + | + | + | − | + | + | + | + |
| Chan et al. 2014 Taiwan64 | + | + | + | − | + | + | + | + |
| Man et al. 2014 Hong Kong65 | + | + | + | − | + | + | − | + |
| Oh et al. 2013 Australia66 | + | + | − | − | − | + | ? | + |
| Wong et al. 2006 Hong Kong67 | + | + | + | − | + | + | ? | + |
| Song et al. 2007 USA68 | + | ? | + | ? | + | ? | ? | + |
| Cameron et al. 2011 Australia69 | + | + | + | − | + | − | ? | − |
| Darbandi et al. 2014 Iran70 | + | ? | + | − | + | + | ? | + |
| Wei et al. 2008 China71 | + | + | + | ? | ? | + | ? | ? |
| Wang et al. 2007 USA72 | + | + | + | − | + | + | ? | + |
| Kvorning et al. 2003 Sweden73 | + | ? | + | − | + | + | ? | + |
| Kvorning et al. 2003 Sweden74 | + | ? | + | − | + | + | ? | + |
| Yang et al.2010 China75 | + | ? | + | − | + | + | + | + |
| Sahmeddini et al.2010 Iran76 | + | + | + | ? | + | + | ? | + |
| Wang et al. 2007 China77 | + | ? | + | − | + | + | ? | ? |
| Jia et al. 2009 China78 | + | ? | + | ? | + | + | ? | − |
| Wang et al. 2013 China79 | + | + | + | − | + | + | + | + |
| Andreescu et al. 2011 Canada80 | + | ? | + | − | + | + | + | + |
| Yeung et al. 2009 Hong Kong81 | + | + | + | − | + | + | ? | − |
| Chen et al. 2014 Taiwan82 | + | ? | + | ? | + | + | ? | + |
| Wang et al. 2008 China83 | + | ? | + | − | + | + | ? | + |
| Meissner et al. 2004 Germany84 | + | + | + | − | + | + | ? | + |
| Zhou et al. 2012 China85 | + | ? | + | − | + | + | ? | + |
| Yeh et al. 2012 Taiwan86 | + | + | + | − | + | + | + | + |
| Yu et al. 2011 Taiwan87 | + | ? | + | − | + | + | ? | + |
| Ma et al. 2011 China88 | + | + | + | − | + | + | ? | + |
| Li et al. 2013 China89 | + | ? | + | ? | + | + | ? | + |
| Deluze et al. 1992 Switzerland90 | + | + | + | − | + | + | ? | − |
| Ng et al. 2013 Hong Kong91 | + | + | + | − | + | + | + | + |
| Lee and Lee 2009 Republic of Korea92 | + | ? | + | − | + | + | ? | + |
| Tam et al. 2007 Hong Kong93 | + | + | + | − | + | − | + | + |
| Kvorning and Akeson 2010 Sweden94 | + | ? | + | − | + | + | ? | + |
| Waite and Clough 1998 UK95 | + | ? | + | ? | + | + | ? | + |
| Holzer et al. 2011 Austria96 | + | ? | + | − | + | + | ? | + |
| Sator-Katzenschlager et al. 2006 Austria97 | + | ? | + | − | + | + | ? | + |
| Liu et al. 2011 China98 | + | + | + | − | + | + | + | − |
| Liu et al. 2014 China99 | + | + | + | − | + | + | + | + |
| Maeda et al. 2013 USA100 | + | ? | + | − | + | + | ? | ? |
| Shi et al. 2011 China101 | + | ? | + | ? | + | + | ? | + |
| Dias et al. 2010 Brazil102 | + | ? | + | ? | + | + | ? | − |
| Zhang et al. 2013 Hong Kong103 | + | ? | + | ? | + | + | ? | + |
| Sangdee et al. 2002 Thailand104 | + | ? | + | − | + | + | ? | + |
| Johansson et al. 2001 Sweden105 | + | + | + | − | + | + | ? | + |
| Hopwood et al. 2008 UK106 | + | + | + | − | + | − | ? | − |
| White et al. 1998 England107 | + | + | + | − | + | − | ? | − |
| Dias et al. 2014 Brazil108 | + | ? | + | − | + | + | ? | − |
| Lin et al. 2013Taiwan109 | + | + | + | − | + | + | ? | + |
| Michalek-Sauberer et al. 2007 Austria110 | + | + | + | − | + | + | ? | − |
| Carlsson and Sjolund 2001 Sweden111 | + | + | + | − | + | + | ? | + |
Note: A, Adequate sequence generation; B, Allocation Concealment; C, Blinding (participants); D, Blinding (personnel); E, Blinding (outcome assessor); F, Incomplete outcome data addressed; G, Free of selective reporting; H, Free of other bias. +, Yes; −, No; ?, Unclear.