Table 2. Results of quality assessment using the Newcastle-Ottawa scale for cohort studies.

	Selection				Comparabiliy	Outcome			Score
	Representativeness of the exposed cohort	Seletion of the non exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability of cohorts on the basis of the design or analysis	Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow up of cohorts
Chen Z 2019	*	*	*	-	-	*	*	*	6
Chen Z 2021	*	*	*	-	*	*	*	*	8
Ji N 2022	*	*	*	-	*	*	*	*	8

A study can be awarded a maximum of one asterisk for each numbered item within the Selection and Outcome categories. A maximum of two asterisks can be given for Comparability.