Table 1.

Characteristics of studies included in the meta-analysis

Reference	Source of controls	Area	Ethnicity	Case no.	Control no.	Case			Control			HWE
						TT	CT	CC	TT	CT	CC	X2	P
Hu 1999 [12]	PB+HB	Guangdong	Han	59	132	22	22	15	34	76	22	3.43	0.064
Persson 1999 [13]	PB	Beijing	Not stated	76	90	33	34	9	36	44	10	0.40	0.526
Song 1999 [14]	PB	Beijing	Not stated	150	391	35	93	22	162	173	56	0.79	0.375
Song 2001 [15]	PB	Beijing	Not stated	217	404	60	129	28	173	175	56	1.19	0.275
Yin 2001 [16]	HB	Jiangsu	Not stated	84	84	36	35	13	28	38	18	0.57	0.451
Zhou 2002 [17]	HB	Hubei	Not stated	92	98	34	43	15	51	34	13	3.29	0.070
Wang 2003 [18]	PB	Beijing + Tianjin	Han	162	181	64	76	22	65	78	38	2.54	0.111
Dong 2004 [19]	HB	Sichuan	Not stated	82	91	35	36	11	46	35	10	0.71	0.401
Liang 2004 [20]	HB	Jiangsu	Han	152	152	50	82	20	70	71	11	1.52	0.218
Li 2004 [21]	HB	Beijing	Not stated	217	200	93	88	36	85	89	26	0.13	0.722
Li 2005 [22]	PB	Henan	Han	103	138	27	64	12	73	54	11	0.05	0.819
Ng 2005 [23]	HB	Singapore	Not stated	124	162	22	61	41	19	87	56	2.87	0.090
Qian 2006 [24]	PB	Tianjin	Han	108	108	45	33	30	44	52	12	0.33	0.563
Tao 2007 [25]	Not stated	Anhui	Not stated	47	94	24	19	4	43	37	14	1.59	0.208
Xia 2008 [26]	HB	Gansu	Han	58	116	17	36	5	40	58	18	0.16	0.688
Zhu 2010 [27]	PB	Hunan	Not stated	160	160	55	68	37	68	66	26	2.08	0.149
Tuerxun 2011 [28]	PB	Xinjiang	Han	59	84	19	27	13	33	45	6	3.19	0.074
Wang 2012 [29]	PB	Henan	Han	209	256	61	106	42	87	120	49	0.44	0.508
Li 2012 [30]	PB	Beijing	Not stated	217	198	93	88	36	83	89	26	0.08	0.781
Huang 2013 [31]	PB	Hunan	Han	168	201	51	83	34	61	93	47	0.99	0.320
Jiang 2014 [32]	PB	Inner Mongolia	Mongolian	142	190	28	59	55	64	95	31	0.18	0.668
Jiang 2014 [32]	PB	Inner Mongolia	Han	180	266	37	71	72	87	126	53	0.36	0.547
Yang 2014 [33]	PB	Hebei	Not stated	150	136	60	64	26	62	56	18	0.87	0.350

PB: Population-based, HB: hospital-based.