Supplementary Table 2.

Quality assessment of cross-sectional studies based on Newcastle-Ottawa quality assessment scale

Author, year	Selection				Comparability	Outcome		Total score
	Representativeness of the sample	Sample size	Nonrespondents	Ascertainment of the exposure	The subjects in different outcome groups are comparable, based on the study design or analysis	Assessment of the outcome	Statistical test
Huang et al. (2010)[28]	*	*	*	**	*	**	*	9
Riazi et al. (2017)[32]	*	*		**	**	**	*	9
Straub et al. (2016)[35]	*	*		**	**	**	*	9
Wan Noor Fatehah et al. (2019)[39]	*	*		**	**	**	*	9