Table 2.

Details of study quality evaluation via the Newcastle-Ottawa Scale.

Study	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Outcome not present at baseline	Control for age	Control for other confounding factors	Assessment of outcome	Enough long follow-up duration	Adequacy of follow-up of cohorts	Total
Kwan et al. (18)	0	1	1	1	1	1	1	1	0	7
Chae et al. (13)	0	1	1	1	1	1	1	1	0	7
Ahern et al. (12)	1	1	1	1	1	1	1	1	1	9
Nielsen et al. (14)	1	1	1	1	1	1	1	0	1	8
Botteri et al. (19)	0	1	1	1	1	1	1	1	0	7
Brewer et al. (15)	1	1	1	1	1	1	1	0	0	7
Boudreau et al. (20)	0	1	1	1	1	1	1	1	0	7
Murtola et al. (16)	1	1	1	1	1	1	1	1	1	9
Cardwell et al. (21)	1	1	1	1	1	1	1	1	0	8
Sakellakis et al. (23)	0	1	0	1	1	1	1	1	0	6
Mc Menamin et al. (22)	0	1	1	1	1	1	1	1	0	7
Smith et al. (25)	0	1	1	1	1	1	1	1	1	8
Shaitelman et al. (24)	0	1	1	1	1	1	1	1	0	7
Tryggvadottir et al. (26)	0	1	1	1	1	1	1	1	0	7
Li et al. (27)	0	1	1	1	1	1	1	1	1	7
Borgquist et al. (17)	1	1	1	1	1	1	1	1	1	9
Bjarnadottir et al. (28)	0	1	1	1	1	1	1	1	1	8