Table 2. Research quality rating scale.

Study	Selection				Comparability		Exposure			Score
	A	B	C	D	E	F	G	H	I
Chiu et al. (2019a), Chiu et al. (2019b)	✓	✓		✓	✓	✓	✓	✓	✓	8
Zhu et al. (2020)	✓	✓		✓	✓		✓	✓	✓	7
Liu et al. (2020)	✓	✓		✓	✓		✓	✓	✓	7
Watts et al. (2021)	✓			✓	✓		✓	✓	✓	6
Zhou et al. (2021)	✓	✓		✓	✓		✓	✓	✓	7
Sahoyama et al. (2022)		✓	✓		✓		✓	✓	✓	6
Lin, Li & Li (2022)	✓	✓	✓	✓	✓		✓	✓	✓	8
Chiu et al. (2023)				✓	✓		✓	✓	✓	5
Zhang et al. (2023)	✓	✓	✓	✓	✓		✓	✓	✓	8
Wan et al. (2023)	✓	✓	✓	✓	✓		✓	✓	✓	8

Notes.

A, adequate case definition or representativeness of the exposed cohort; B, representativeness of cases or selection of non-exposed queues; C, selection of controls or determination of exposure; D, definition of controls or no outcome event occurred before the start of the research object; E, controlled for age; F, controlled for additional factors; G, ascertainment of exposure or evaluation of outcome events; H, same method for cases and controls or adequacy of follow-up; I, non-response rate or integrity of follow-up.