Table 3. Quality assessments of cohort studies with Newcastle-Ottawa Scale (NOS) (N = 13).

Study ID	Representativeness of the exposed cohort	Selection of the non exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at baseline	Comparability of cohorts on the basis of the design or analysis	Assessment of outcome	Was follow-up long enough for outcomes' occur	Adequacy of follow up of cohorts	NOS quality score (Num. of stars)
Zelefsky et al. 2010 [16]	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Merino et al. 2013 [17]	⋆	⋆	⋆	⋆	NA	⋆	⋆	⋆	7
Tewari et al. 2007 [18]	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Kibel et al. 2012 [19]	⋆	⋆	⋆	⋆	NA	⋆	⋆	⋆	7
Stokes et al. 2000 [20]	⋆	⋆	⋆	⋆	NA	⋆	⋆	⋆	7
Cooperberg et al. 2010 [21]	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Bastide et al. 2011 [23]	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Koie et al. 2014 [24]	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Lee et al. 2014 [25]	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Hsu et al. 2006 [26]	⋆	⋆	⋆	⋆	⋆	⋆	⋆	⋆	8
Westover et al. 2012 [27]	⋆	⋆	⋆	⋆	⋆⋆	⋆	⋆	⋆	9
Galalae et al. 2004 [28]	⋆	⋆	⋆	⋆	NA	⋆	⋆	⋆	7
Demanes et al. 2009 [29]	⋆	⋆	⋆	⋆	NA	⋆	⋆	⋆	7

The full mark for NOS was 9-point. Scores ≥7 was considered with high-quality. NA: Not Available.