Table 3.

Quality analysis of the studies using the Newcastle–Ottawa Scale for cross-sectional studies [29].

Authors	Selection Items				Comparability Items	Outcomes Items		Total Score/9
	1	2	3	4	5	6	7
Gerlovin et al., 2019 [22]	*	*	*			*	**	6/9
Kei et al., 2015 [35]	*	*	*			*	**	6/9

Selection: 1: Representativeness of the sample (1 point); 2: Sample size (1 point); 3: Non-respondents (1 point); 4: Ascertainment of exposure (2 points); 5: Comparability: subjects in different outcomes are comparable, based on the study design or analysis, and confounding factors are controlled (1 point); 6: Outcome: Assessment of the outcome (2 points); 7: Statistical test (1 point). *: Corresponds to 1 point from the total score when the research adequately meets the item. * 1 point; ** 2 points of the total score.