Table 4.

Quality assessment using Newcastle–Ottawa Scale (NOS).

References	Selection (out of 4)				Comparability (out of 2)	Outcomes (out of 3)			NOS score
	Representativeness of exposed cohort	Selection of non-exposed cohort	Exposure	Outcome of interest not present at start		Assessment of outcome	Follow-up	Adequacy of follow-up
Kanazawa et al. (14)	*	*	*	*	**	*	Unclear	Unclear	7
Chan et al. (15)	*	*	*	*	**	*	Unclear	Unclear	7
Zhang et al. (16)	*	*	*	*	**	*	*	Unclear	8
Hallet et al. (18)	*	*	*	*	**	*	*	Unclear	8
Liu et al. (17)	*	*	*	*	**	*	*	Unclear	8
Noda et al. (19)	*	*	*	*	**	*	Unclear	Unclear	7
Ome et al. (20)	*	*	*	*	**	*	Unclear	Unclear	7
Goh et al. (21)	*	*	*	*	**	*	*	Unclear	8
Inoue et al. (22)	*	*	*	*	**	*	Unclear	Unclear	7
van der Poel et al. (23)	*	*	*	*	**	*	Unclear	Unclear	7
Onoe et al. (24)	*	*	*	*	**	*	Unclear	Unclear	7
Morise et al. (25)	*	*	*	*	**	*	*	Unclear	8