Table 2.

Quality assessment of the included studies based on the Newcastle-Ottawa scale (NOS)

Study	Selection				Comparability	Outcome		Overall Score
	Representation	Sample Size	Non-Respondents	Exposure		Outcome	Statistical Test
Amadio et al	*	*	*	**	**	**	*	10
Aslan et al	*	*	*	**	0	**	*	8
Bai et al	*	*	*	**	**	**	*	10
Ejiri et al	*	*	*	**	0	**	*	8
Esmaeili et al	*	*	*	**	**	**	*	10
Forent et al	*	*	*	**	**	**	*	10
Han et al	*	*	*	**	**	**	*	10
Jin et al	*	*	*	**	**	**	*	10
Monisha et al	*	*	*	**	0	**	*	8
Sustar et al	*	*	*	**	**	**	*	10
Wu et al	*	*	*	**	**	**	*	10
Xia et al	*	*	*	**	0	**	*	8