Table 1.

The Newcastle-Ottawa Quality Assessment Scale for case-control studies.

Study	Selection	Comparability	Outcome	Summary
Bokhari FA (2012)	4	2	2	8
Hiroyasu I (2004)	3	2	2	7
Fang X (2005)	4	2	2	8
Li ZH (2003)	4	2	2	8
Araki A (1989)	4	2	2	8
Perini F (2005)	4	2	2	8
Peng H (2000)	4	2	2	8