(b).

CCS	Selection				Comparability	Exposure
	Adequate definition of cases	Representativeness of cases	Selection of controls	Definition of controls	Control for important factor or additional factor	Ascertainment of exposure	Same method of ascertainment for cases and controls	Nonresponse rate	Total score
Manfredini et al. [34]	∗	∗	∗	∗			∗		5
Ferruzzi et al. [35]	∗	∗	∗	∗	∗		∗		6
Macmull et al. [36]		∗	∗		∗		∗		4
Panagopoulos et al. [37]	∗	∗	∗	∗			∗		5

^†Follow-up > 4 years. CS: cohort study; CCS: case-control study.