Table 2. Data extraction from case-control studies and nested case-control studies.

Study	Sample	Case group				Control group
		HP+a	HP−b	Nc		HP+	HP−	N
Permuth	262	13	118	131		16	115	131
Geng	138	47	21	68		34	36	70
Huang	896	196	250	448		206	241	448
Ai	116	36	20	56		28	32	60
Risch	1,555	233	528	761		327	467	794
Yu	706	325	28	353		328	25	353
Gawin	316	121	18	139		146	31	177
Risch	1,063	80	293	373		120	570	690
Lindkvist	350	39	48	87		100	163	263
Dou	221	54	31	85		64	72	136
de Martel	366	51	53	104		155	107	262
Stolzenberg-Solomon	347	99	22	121		165	61	226
Raderer	119	60	32	92		12	15	27

^a, the number of patients with H. pylori infection; ^b, the number of patients without H. pylori infection; ^c, overall number of patients. HP, Helicobacter pylori.