Table 3.

Assessment of study quality included in the meta-analysis by Newcastle Ottawa Scale (NOS) for case-control studies

Source	Selection				Comparabilitya		Exposure			Total scores
	1	2	3	4	5A	5B	6	7	8
Mourouti et al.	*	*	*	*	*	*	*	*	–	8
Tajaddini et al.	*	*	–	*	*	*	*	*	–	7
Yun et al	*	*	–	–	*	*	*	*	–	6
Adzersen et al.	*	*	–	*	*	*	–	*	–	6
Chatenoud et al.	*	*	–	*	*	*	–	*	*	7
Levi et al.	*	–	–	*	*	*	*	*	*	7
LaVecchia et al	*	*	–	*	*	*	*	*	*	8

1 Is the case definition adequate? 2 Representativeness of the cases. 3 Selection of controls. 4 Definition of controls. 5 Comparability of cases and controls on the basis of the design or analysis. 6 Ascertainment of exposure. 7 Same method of ascertainment for cases and controls. 8 Non-response rate

^aStudies that controlled for age and traditional risk factors received one score, whereas studies that controlled for other important confounders received an additional score