Table 2.

New Castle–Ottawa Scale ratings. Each asterisk represents one point.

Reference	Selection	Comparability	Exposure/outcome
Adhikari et al. (14)	****	–	***
Byvaltsev et al. (15)	****	–	**
Delgado-López et al. (16)	****	*	**
Devin et al. (17)	****	*	**
Dewan et al. (18)	****	*	***
Emohare et al. (19)	****	–	**
Garg et al. (20)	****	**	***
Gun-Ill et al. (21)	****	*	**
Haimoto et al. (22)	****	**	***
Heller et al. (23)	****	*	***
Hill et al. (24)	****	–	**
Li et al. (25)	****	**	***
Liu et al. (26)	****	**	***
Maajid et al. (27)	****	**	***
Martin et al. (28)	****	**	**
Martin et al. (29)	****	**	**
Oktay et al. (30)	****	**	***
Pahys et al. (31)	****	**	***
Strom et al. (33) (cervical)	****	**	***
Strom et al. (32)	****	**	***
Sweet et al. (34)	****	**	***
Takeuchi et al. (35)	****	**	***