Table 2.

Assessment of methodological quality of observational cohort studies, according to the Newcastle–Ottawa scale.

Author/Year	Selection				Comparability			Outcome
	Representative of the Exposed Cohort	Selection of External Control	Ascertainment of Exposure	Outcome of Interest Not Present at the Start of the Study	Main Factor	Additional Factor	Assessment of Outcomes	Sufficient Follow-Up Time	Adequacy of Follow-Up	Total
Michaud et al., 2008 [21]	*		*	*			*	*	*	6/9
Huang et al., 2019 [23]	*	*	*	*	*		*	*	*	8/9
Michaud et al., 2016 [22]	*		*	*			*	*	*	6/9
Lee et al., 2017 [24]	*		*	*			*	*	*	6/9

*: Means that the response is affirmative.