Table 2. Risk of bias assessment using the Newcastle-Ottawa Scale.

Study	Newcastle-Ottawa Scale			Overall risk of bias
	Selection	Comparability	Exposure
Huang et al., 2020	***	*	*	Low
Guan et al., 2020	***	*	**	Moderate
Zheng et al., 2020	****	*	*	Low
Wang et al., 2020	***	*	**	Moderate
Chen et al., 2020	**	*	*	High
Hong et al., 2020	**	*	**	High
Wang et al., 2020	**	*	**	High
Mo et al., 2020	**	*	*	High
Wu et al., 2020	***	*	**	Moderate
Zhou et al., 2020	***	*	*	Moderate
Wang et al., 2020	***	*	**	Moderate
Huang et al., 2020	****	*	*	Low
Colaneri et al., 2020	***	*	**	Moderate
Goyal et al., 2020	**	*	*	High
Ruan et al., 2020	**	*	*	High
Rong-Hui Du et al., 2020	****	*	*	Low
Qin et al., 2020	***	*	**	Moderate
Paranjpe et al., 2020	****	*	*	Low
Zheng et al., 2020	***	*	**	Moderate
Zhang et al., 2020	***	*	*	Moderate
Mikami et al., 2020	***	*	**	Moderate
Marcello et al., 2020	***	*	**	Moderate
Wang et al., 2020	****	*	*	Low
Cao et al., 2020	**	*	*	High
Shahriarirad et al., 2020	***	*	*	Moderate
Suleyman et al., 2020	**	*	*	High
Khamis et al., 2020	****	*	*	Low
Zhang et al., 2020	***	*	*	Moderate
Yang et al., 2020	***	*	*	Moderate