Table 4.

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

Source	Selection				Comparabilitya		Outcome			Total scores
	1	2	3	4	5A	5B	6	7 b	8 c
Farvid et al	–	*	*	*	*	*	*	*	*	8
Egeberg et al.	*	*	–	*	*	*	*	*	–	7
Sonestedt et al	*	*	*	*	*	*	*	*	*	9
Nicodemus et al.	*	*	*	*	*	*	*	*	–	8

1 Representativeness of the exposed cohort. 2 Selection of the non-exposed cohort. 3 Ascertainment of exposure for cohort studies. 4 Demonstration that outcome of interest was not present at start of study for cohort studies. 5 Comparability of cohorts on the basis of the design or analysis. 6 Assessment of outcome. 7 Was follow-up long enough for outcomes to occur. 8 Adequacy of follow up of cohorts

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

^bstudy with follow-up time > 2 years was assigned one score

^cstudy with follow-up rate > 70% was assigned one score