Table 1. Study characteristics.

	First author	Study location	Yeara	Number of cases/controls	Source of control selection	% −308A allele frequencyb	% −238A allele frequencyc	% −857T allele frequencyd	P, HWE −308e	P, HWE −238f	P, HWE −857g
1	Jang	Korea (E)	2001	52/92	Healthy volunteers	3.8	7.1	—	0.70	0.39	—
2	Wu	Taiwan (E)	2002	150/220	Healthy volunteers	12.0	1.8	—	<0.01	<0.01	—
3	El-Omar	USA (W)	2003	314/210	Population based	15.2	—	—	0.55	—	—
4	Machado	Portugal (W)	2003	287/304	Healthy volunteers	12.7	—	—	0.65	—	—
5	Fei	China (E)	2004	56/164	Healthy volunteers	6.7	—	—	0.12	—	—
6	Glas	Germany (W)	2004	88/145	Healthy volunteers	15.2	3.8	—	0.67	0.63	—
7	Lee SG	Korea (E)	2004	341/261	Healthy volunteers	8.4	4.8	15.9	0.49	0.42	0.85
8	Torres	Colombia (W)	2004	44/66	Clinic based	7.6	—	—	0.51	—	—
9	Wu	Taiwan (E)	2004	204/210	Healthy volunteers	12.4	1.7	14.3	<0.01	<0.01	0.20
10	Ohayama	Japan (E)	2004	300/472	Clinic based	—	—	18.6	—	—	0.90
11	Garza-Gonzalez	Mexico (W)	2005	63/215	Clinic based	8.6	—	—	0.61	—	—
12	Guo	China (E)	2005	264/437	Healthy volunteers	5.9	—	—	<0.01	—	—
13	Lee JY	Korea (E)	2005	122/120	Healthy volunteers	7.1	—	—	0.40	—	—
14	Li	China (E)	2005	59/264	Healthy volunteers	7.2	—	—	0.56	—	—
15	Lu	China (E)	2005	250/300	Population based	4.7	3.8	—	0.08	0.49	—
16	Perri	Italy (W)	2005	184/362	Healthy volunteers	10.9	—	—	0.15	—	—
17	Rocha	Brazil (W)	2005	161/535	Healthy volunteers	13.9	—	—	0.34	—	—
18	Zambon	Italy (W)	2005	129/644	Clinic based	12.3	5.9	19.6	0.90	0.38	<0.01
19	Kamangar	Finland (W)	2006	112/208	Healthy cohort subjects	13.5	1.2	—	0.29	0.86	—
20	Kim	Korea (E)	2006	237/461	Healthy volunteers	6.8	—	—	0.91	—	—
21	Morgan	Honduras (W)	2006	168/161	Population based	3.7	—	—	0.62	—	—
22	Hou	Poland (W)	2007	305/427	Population based	16.2	—	—	0.19	—	—
23	Sugimoto	Japan (E)	2007	105/172	Clinic based	0.9	—	15.7	0.91	—	0.11
24	Garcia-Gonzalez	Spain (W)	2007	404/404	Healthy volunteers	11.3	10.3	—	0.35	0.01	—

E=East Asian country; HWE=Hardy–Weinberg equilibrium; TNF-A=tumour-necrosis factor-A; W=western country.

^aYear: Publication year.

^bPercentage of TNF-A –308A allele frequency among controls.

^cPercentage of TNF-A –238 A allele frequency among controls.

^dPercentage of TNF-A –857 T allele frequency among controls.

^eP-value for HWE for TNF-A –308 polymorphism among controls.

^fP-value for HWE for TNF-A –238 polymorphism among controls.

^gP-value for HWE for TNF-A –857 polymorphism among controls.