Table 3.

Quality assessment of included studies.

References	Study type	Selection				Comparability	Exposure/Outcome			Final score
		Item 1	Item 2	Item 3	Item 4	Item 5	Item 6	Item 7	Item 8
Curro et al. (35)	Case-control study	1	0	1	1	1	0	1	0	5
Atteritano et al. (34)	Case-control study	1	1	1	1	2	0	1	0	7
Janbakhsh et al. (28)	Case-control study	1	0	1	1	1	0	1	0	5
Zhang et al. (33)	Cohort study	0	1	1	1	1	1	1	0	6
Zhang et al. (36)	Cohort study	1	1	1	1	1	1	1	1	8
Hileman et al. (31)	Cohort study	1	0	0	1	1	1	1	1	6

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

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