Table 1

Results of the quality assessment of the 22 included articles

Author and year of publicationStudy ParticipationStudy AttritionOutcome MeasurementStatistical Analysis and ReportingRisk of bias assessment
General population studies
 Abujam et al. 2014 [49]NoN/AYesYesHigh
 Adams et al. 2013 [35]YesN/AYesYesLow
 Auvinen et al. 2009 [50]NoN/APartlyYesHigh
 Bishop et al. 2012 [51]NoN/AYesYesHigh
 Diepenmaat et al. 2006 [36]YesN/AYesYesLow
 Ehrmann Feldman et al. 2002 [37]YesYesPartlyYesLow
 El-Metwally et al. 2006 [15]YesN/AYesYesLow
 Hoftun et al. 2011 [38]YesN/AYesYesLow
 Hulsegge et al. 2011 [47]PartlyYesPartlyYesMedium
 Jespersen et al. 2014 [14]YesYesYesYesLow
 Jespersen et al. 2015 [39]YesN/AYesYesLow
 Krul et al. 2009 [40]YesN/AYesYesLow
 Mikkelsson et al. 1997 [41]YesN/AYesYesLow
 Molgaard et al. 2011 [48]PartlyN/AYesYesMedium
 Rathleff et al. 2013 [42]YesN/AYesYesLow
 Shrier et al. 2001 [43]YesYesPartlyYesLow
 Slowinska et al. 2015 [68]NoN/AYesPartlyHigh
 Smedbraten et al. 1998 [52]NoN/AYesYesHigh
 Verhagen et al. 2009 [54]YesNoYesYesHigh
Clinical studies
 Bot et al. 2005 [44]YesN/Aa YesPartlyLow
 Henschke et al. 2014 [45]YesN/Aa YesYesLow
 Van der Waal et al. 2006 [46]YesN/Aa YesYesLow
aAttrition bias may be present, but very small.
If present, it will be on general practitioners level, and not on patient level