Study Year of
publication 		Random sequence generation Allocation concealment Blinding Incomplete outcome data Selective reporting Other bias
Deppe et al. [22] 2007 ? ? ? - + +
Roos-Jansåker et al. [23] 2007 ? ? + - ? +
Roos-Jansåker et al. [24] 2007 ? ? ? - ? +
Schwarz et al. [25] 2008 + ? + - ? +
Romanos et al. [26] 2008 ? ? ? - - -
Schwarz et al. [27] 2009 + ? + - ? +
Schwarz et al. [28] 2010 ? ? + - ? +
Roccuzzo et al. [29] 2011 ? ? + + ? +
Froum et al. [30] 2012 ? ? + - - -
Aghazadeh et al. [31] 2012 + - + + + +
Wohlfahrt et al. [32] 2012 + + + + + +
Wiltfang et al. [33] 2012 ? ? ? - - +
Schwarz et al. [34] 2013 + ? + ? - +
Matarasso et al. [35] 2014 ? ? ? - ? +
Roos-Jansåker et al. [36] 2014 ? ? + - ? +
Jepsen et al. [37] 2015 + + + + + +
Froum et al. [38] 2015 ? ? + + + -
Roccuzzo et al. [39] 2016 ? ? - + + +

+ = low risk; ? = unclear risk; - = high risk.