Table 1.

Birth data and observed/expected cases of inflammatory bowel disease in the United Kingdom

	Jan	Feb	Mar	Apr	May	June	July	Aug	Sept	Oct	Nov	Dec
UK births 1978–98 (thousands)	1302	1202	1336	1296	1355	1327	1377	1344	1339	1330	1245	1257
CD cases observed	69	45	44	59	49	58	59	56	61	43	52	39
CD cases expected	52	48	54	52	55	53	55	54	54	54	50	50
“Rate” of CD per 100000 births	5.3	3.7	3.3	4.6	3.6	4.4	4.3	4.2	4.6	3.2	4.2	3.1
UC cases observed	26	26	23	17	29	20	20	25	20	24	20	27
UC cases expected	23	21	24	23	24	23	24	24	24	23	22	22
“Rate” of UC per 100000 births	2.0	2.2	1.7	1.3	2.1	1.5	1.5	1.9	1.5	1.8	1.6	2.2
IBD cases observed	103	81	80	88	88	91	88	92	89	80	82	78
IBD cases expected	86	79	87	86	90	87	91	89	89	88	82	83
“Rate” of all IBD per 100000 births	7.9	6.7	6.0	6.8	6.5	6.9	6.4	6.8	6.6	6.0	6.6	6.2

CD, Crohn’s disease; UC, ulcerative colitis; IBD, all cases of inflammatory bowel disease. Expected, the number of cases that would have been born in the calendar month if all differences in the number of cases per month were attributable to variation in the total number of births. “Rates”, calculated from the observed cases and total births. See text for definition of “rate”.