Author/ Year Selection of participants Confounding Variables Measurement of exposure Blinding of outcome assessments Incomplete outcome data Selective outcome reporting Lonbro et al., 2013 [13] High risk Unclear Low risk Unclear Low risk Low risk Eades et al., 2013 [20] High risk High risk Low risk High risk Low risk Low risk Aghili et al. 2007 [21] Unclear Unclear High risk Unclear Low risk Unclear Crevenna et al., 2003 [22] Unclear High risk Low risk High risk Low risk Low risk Duffy et al., 2009 [24] Low risk Low risk High risk Unclear Low risk Low risk Duffy et al., 2008 [23] Low risk Low risk High risk Unclear Low risk Low risk Silver et al., 2007 [25] Low risk Unclear Low risk High risk Low risk Low risk

Table 3: Risk of bias of included non-randomized studies. Tool used: The Risk of Bias Assessment tool for Non-randomized Studies (RoBANS) [17]