Table 2. NOS for risk of bias assessment in included studies.

Studies	Selection (maximum four stars)	Comparability (maximum two stars)	Outcome (maximum three stars)	Total
Gasser et al.	***	–	**	5
Huckaby et al.	***	**	***	8
Liu et al.	**	**	*	5
Li et al.	***	**	***	8
Norton et al.	***	**	***	8
Rios et al.	**	–	*	3
Sabashnikov et al.	**	**	**	6
Suzuki et al.	***	**	***	8
Yousef et al.	***	**	***	8
Conway et al.	***	–	***	6
Friedrich et al.	***	**	***	8
Fukui et al.	****	**	***	9
Chen et al.	***	**	***	8
Santamaria et al.	***	**	***	8
Hirata et al.	**	*	**	5

Total scores greater or equal to six were considered moderate to good quality. NOS, Newcastle-Ottawa Scale.