Table 2.

Quality assessment of studies using the Newcastle-Ottawa scale.

Studies	Selection	Comparability	Exposure	Total
Arunachalan et al.	3	2	2	7
Chi et al.	4	2	2	8
Galani et al.	4	2	2	8
Hadjadj et al.	4	2	2	8
Henry et al.	4	2	1	7
Kwon et al.	4	2	2	8
Liu et al.	4	2	2	8
Lucas et al.	4	2	2	8
Ruetsch et al.	3	2	2	7
Sánchez-Cerrillo et al.	4	2	2	8
Silvin et al.	4	2	2	8
Tincati et al.	4	2	2	8
Turnbull et al.	4	2	2	8
Thwaites et al.	3	2	2	7
Yang et al.	4	2	1	7