Table 2.

Quality of included studies according to Newcastle–Ottawa Scale (NOS).

Case–control studies
Publications	Case definition adequate	Representativeness of the cases	Selection of controls	Definition of controls	Comparability of cases and controls	Ascertainment of exposure	Same method of ascertainment	Non-response rate	NOS
Chen et al. (2017)	*	*	–	*	**	*	*	*	8
Fang et al. (2016)	*	*	*	*	**	*	*	*	9
Rahim et al. (2018)	*	*	*	*	**	*	*	*	9
Zhou et al. (2019)	*	*	*	*	_	*	*	*	7

Cross sectional studies
Publications	Representativeness of the sample	Sample size	Non-respondents	Ascertainment of the exposure	Comparability	Ascertainment of outcome	Statistical test		NOS
Kieboom et al. (2017)	*	–	*	*	–	**	*		6
Lind et al. (1990)	*	–	*	*	**	–	*		6
Yadav et al. (2017)	*	–	*	*	*	**	*		7
Spiga et al. (2019)	*	–	*	*	–	*	*		5
Chambers et al. (2006)	*	–	*	*	–	*	*		5
Aksit et al. (2019)	*	–	*	*	–	**	*		5