Table I.

Characteristics of studies included in the present meta-analysis.

				Genotypic distribution
				Case		Control		Newcastle-Ottawa scale
Reference	Year	Country	Controls	Null	Present	Null	Present	Selectiona	Comparabilityb	Assessmenta	Total
Piao et al (17)	2013	Korean	HB	2070	1863	858	841	3	2	2	7
Wang et al (27)	2012	China	PB	90	119	100	156	3	2	2	7
Liang et al (41)	2012	China	HB	45	23	34	36	2	0	2	4
Kiyohara et al (15)	2012	Japan	PB	217	245	164	215	3	2	4	9
Liu (34)	2011	China	HB	57	43	56	79	3	0	3	6
Tamaki et al (26)	2011	Japan	PB	97	95	104	99	3	1	3	7
Fang (33)	2011	China	HB	45	23	34	36	3	0	2	5
Du (31)	2011	China	HB	57	68	56	69	3	1	2	6
Bai (29)	2011	China	HB	56	72	96	118	3	1	2	6
Fan et al (39)	2010	China	HB	38	20	29	31	3	2	2	7
Qi et al (37)	2008	China	HB	17	36	27	45	3	2	2	7
Yang et al (25)	2007	Korea	HB	168	148	166	179	3	2	2	7
Li (30)	2007	China	HB	17	25	48	55	3	1	2	6
Lee et al (23)	2006	Korea	HB	80	89	107	89	2	2	2	6
He and Tang (35)	2006	China	PB	33	28	29	17	4	0	3	7
Chen et al (20)	2006	China	PB	59	38	85	112	3	0	2	5
Yuan et al (28)	2005	China	HB	82	68	58	94	3	1	2	6
Cao et al (40)	2004	China	HB	69	35	87	118	2	1	2	5
Chan-Yeung et al (19)	2004	China	PB	143	86	102	95	4	2	2	8
Wang et al (5)	2003	China	NR	53	59	54	65	2	1	3	6
Wang (32)	2003	China	HB	44	33	54	53	3	0	3	6
Zhang (38)	2002	China	PB	74	87	72	93	3	2	3	8
London et al (24)	2000	China	PB	134	98	426	284	4	2	3	9
Lan et al (22)	2000	China	PB	73	49	64	58	3	2	3	8
Kiyohara et al (22)	2000	Japan	NR	47	14	39	12	3	2	4	9
Lan et al (37)	1991	China	PB	52	34	52	34	4	2	2	8

^aMaximum score, 4;

^bmaximum score, 2.

HB, hospital-based; PB, population-based.