Table 2.

Results of study quality appraisal of the included studies.

Study	Total score	Selection				Comparability	Outcome
		Representativeness of the sample	Sample size	Non-respondents	Ascertainments of exposure	Based on design and analysis	Assessment of outcome	Statistical test
Ahmed et al., 2020	6	*			*	**	*	*
Gao, 2020	6	*			*	**	*	*
González-Sanguino et al., 2020	4	*			*		*	*
Huang 2020	6	*			*	**	*	*
Lei et al., 2020	7	*		*	*	**	*	*
Liu,  2020	8	*	*	*	*	**	*	*
Mazza et al., 2020	7	*		*	*	**	*	*
Moccia et al., 2020	7	*	*		*	**	*	*
Moghanibashi-Mansourieh 2020	6	*			*	**	*	*
Olagoke et al., 2020	6	*			*	**	*	*
Ozamiz-Etxebarria 2020	5	*			*	**	*
Özdin et al., 2020	7	*	*		*	**	*	*
Qiu et al., 2020	4	*			*		*	*
Samadarshi et al., 2020	7	*	*		*	**	*	*
Sønderskov 2020	5	*			*	*	*	*
Wang et al., 2020	6	*			*	**	*	*
Wang et al., 2020a	6	*			*	**	*	*
Wang et al., 2020b	7	*		*	*	**	*	*
Zhang 2020	7	*		*	*	**	*	*