Table 4

Study quality assessment: Newcastle-Ottawa Scale

	Selection				Comparability	Exposure
	Adequate case definition	Cases representative	Selection of controls	Definition of controls	Comparability of design and analysis	Ascertainment of exposure	Same method of ascertainment	Non-response rate	Total stars
Bankier et al 38	◊	–	◊	◊	◊◊	◊	◊	◊	8
Copeland et al 39	◊	◊	◊	◊	◊◊	◊	◊	–	8
De Berardis et al 42	◊	–	NA	NA	NA	◊	NA	–	2
Hoge et al 44	◊	–	NA	NA	NA	◊	NA	–	2
Hou et al 47	◊	◊	◊	◊	◊◊	◊	◊	–	8
Khandaker et al 33	◊	◊	◊	◊	◊◊	◊	◊	◊	9
Korkeila et al 40	◊	–	◊	–	◊	–	◊	–	4
Nayek and Ghosh34	◊	–	◊	–	◊◊	◊	◊	–	6
Ogłodek et al 48	◊	–	◊	◊	◊◊	–	◊	–	6
Tang et al 35	◊	◊	◊	◊	◊◊	◊	◊	–	8
Tofani et al 46	◊	–	–	–	◊	◊	◊	–	4
Vogelzangs et al 36	◊	◊	◊	◊	◊◊	◊	◊	◊	9
Yang et al 45	◊	◊	–	◊	◊◊	◊	◊	–	7
Zahm41	◊	–	–	–	◊◊	◊	◊	–	5

–, did not meet the criteria; ◊, met criteria for allocation of point on Newcastle-Ottawa scale; ◊◊ , two points on Newcastle-Ottawa scale; NA, not applicable.