Table 7.

Assessment of case–control studies using the Newcastle–Ottawa scale

Study	Selection				Comparability	Exposure			∑
	Question				Question	Questions
	(1)	(2)	(3)	(4)	(1)	(1)	(2)	(3)
[55]	*				*	*		*	4
[65]	*				*	*	*	*	5
[58]			*		*	(*)	*		4
[56]		*	*	*	*	*	*		6
[63]		*	*	*	*	*	*	*	7
[20]		*	*	*	*	*	*		6
[68]		*	*	*	*	*	*	*	7
[66]		*	*	*	*	*	*		6