Table 1

Results of the quality assessment of the 22 included articles

Author and year of publication	Study Participation	Study Attrition	Outcome Measurement	Statistical Analysis and Reporting	Risk of bias assessment
General population studies
Abujam et al. 2014 [49]	No	N/A	Yes	Yes	High
Adams et al. 2013 [35]	Yes	N/A	Yes	Yes	Low
Auvinen et al. 2009 [50]	No	N/A	Partly	Yes	High
Bishop et al. 2012 [51]	No	N/A	Yes	Yes	High
Diepenmaat et al. 2006 [36]	Yes	N/A	Yes	Yes	Low
Ehrmann Feldman et al. 2002 [37]	Yes	Yes	Partly	Yes	Low
El-Metwally et al. 2006 [15]	Yes	N/A	Yes	Yes	Low
Hoftun et al. 2011 [38]	Yes	N/A	Yes	Yes	Low
Hulsegge et al. 2011 [47]	Partly	Yes	Partly	Yes	Medium
Jespersen et al. 2014 [14]	Yes	Yes	Yes	Yes	Low
Jespersen et al. 2015 [39]	Yes	N/A	Yes	Yes	Low
Krul et al. 2009 [40]	Yes	N/A	Yes	Yes	Low
Mikkelsson et al. 1997 [41]	Yes	N/A	Yes	Yes	Low
Molgaard et al. 2011 [48]	Partly	N/A	Yes	Yes	Medium
Rathleff et al. 2013 [42]	Yes	N/A	Yes	Yes	Low
Shrier et al. 2001 [43]	Yes	Yes	Partly	Yes	Low
Slowinska et al. 2015 [68]	No	N/A	Yes	Partly	High
Smedbraten et al. 1998 [52]	No	N/A	Yes	Yes	High
Verhagen et al. 2009 [54]	Yes	No	Yes	Yes	High
Clinical studies
Bot et al. 2005 [44]	Yes	N/Aa	Yes	Partly	Low
Henschke et al. 2014 [45]	Yes	N/Aa	Yes	Yes	Low
Van der Waal et al. 2006 [46]	Yes	N/Aa	Yes	Yes	Low

^aAttrition bias may be present, but very small.
If present, it will be on general practitioners level, and not on patient level