Supplementary Table 2. The Newcastle-Ottawa Scale for assessing qualities of 19 included cohort studies.

Study	Selection (score)				Comparability (score)	Outcome(score)			Total score
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Outcome interest not present at start of study	Control of cohorts on the basis of the design or analysis	Assessment of outcome	Follow-up long enough for outcomes to occur	Adequacy of follow-up of cohorts
Possover et al. (2000) [16]	1	1	1	1	1	1	1	0	9
Trimbos et al. (2001) [7]	0	0	1	1	1	1	0	0	4
Querleu et al. (2002) [21]	1	1	1	0	1	1	1	1	7
Todo et al. (2006) [22]	1	0	1	1	2	1	1	1	8
Raspagliesi et al. (2006) [10]	1	1	1	0	2	1	1	0	7
Pieterse et al. (2008) [9]	0	0	1	1	1	1	1	0	5
Van den Tillaart et al. (2009) [17]	1	1	1	1	2	1	1	1	9
Cibula et al. (2010) [23]	1	0	1	0	2	1	1	1	7
Espino-Strebel et al. (2010) [24]	1	1	1	1	1	1	1	1	8
Liang et al. (2010) [25]	1	1	1	1	2	1	1	1	9
Skret-Magierlo et al. (2010) [18]	0	0	1	1	2	1	1	1	7
Cibula et al. (2011) [26]	0	0	1	1	0	1	1	1	5
Ditto et al. (2011) [27]	1	1	1	0	2	1	1	1	8
Ceccaroni et al. (2012) [28]	1	1	1	1	2	1	1	1	9
Tseng et al. (2012) [19]	0	0	1	1	2	1	1	1	7
Pieterse et al. (2013) [29]	1	1	1	1	2	1	1	1	9
Bogani et al. (2014) [20]	1	1	1	1	2	1	1	1	9
Wang et al. (2014) [30]	1	1	1	1	2	1	1	1	9