Table 5.

Quality assessment for 18 cohort studies

Author	Selection				Comparability		Outcome			Total
	Exposed cohort	Non-exposed cohort	Ascertainment of exposure	Outcome of interest not present at start	Main factors	Additional factors	Assessment of outcome	Follow-up long enough*	Adequacy of follow-up
Katsogridaki, Tzovaras [32]	*	*	*	0	*	*	0	0	*	6
Nance, Eagon [19]	*	*	*	0	*	*	*	*	*	8
Gero, Dib [20]	*	*	*	0	*	0	*	*	*	7
El Labban, Safadi [18]	*	0	*	0	*	*	*	*	*	7
Zerrweck, Zurita [16]	*	0	*	0	*	*	*	*	*	7
Billeter, Probst [25]	*	0	*	*	*	*	*	*	*	8
Papamargaritis [22]	*	0	*	*	*	*	*	*	*	8
Wang, [17]	*	*	*	0	*	0	*	*	*	7
Graham, Murty [5]	*	0	*	0	*	0	*	*	*	6
Gobato, Seixas Chaves [28]	*	0	*	*	*	0	*	*	0	6
Balsa [23]	*	0	*	0	*	*	*	*	*	7
Salle [24]	*	0	*	0	*	*	*	*	*	7
Madan, Orth [26]	*	0	*	0	0	0	*	*	*	5
Burge, Schaumburg [15]	*	0	0	0	0	*	*	0	0	3
Dalcanale, Oliveira [30]	*	0	*	0	*	*	*	*	*	7
Pech, Meyer [31]	*	0	*	*	*	*	*	*	*	8
Pires, Martins [29]	*	0	*	*	*	0	*	*	0	6
Tichansky, [6]	*	0	*	0	0	0	*	0	0	3