Table 3. Observed and expected numbers of colon and rectal cancers, and corresponding standardised incidence ratios in patients with irritable bowel syndrome diagnosed in 1977–1994 and 1995–2008.

	1977–1994			1995–2008
	Observed cancers, N	Expected cancers, N	SIR (95% CI)	Observed cancers, N	Expected cancers, N	SIR (95% CI)
Colon cancer
Total	256	221.1	1.16 (1.02–1.31)	151	137.5	1.10 (0.93–1.29)
Follow-up
⩽3 months	22	2.7	8.03 (5.03–12.16)	42	4.9	8.63 (6.22–11.67)
4–12 months	21	8.5	2.48 (1.53–3.79)	13	14.4	0.91 (0.48–1.55)
2nd and 3rd year	33	22.5	1.47 (1.01–2.06)	29	34.9	0.83 (0.56–1.19)
4th and 5th year	20	22.0	0.91 (0.56–1.40)	21	28.8	0.73 (0.45–1.12)
6th to 10th year	48	51.1	0.94 (0.69–1.25)	41	44.2	0.93 (0.67–1.26)
>10 years	112	114.3	0.98 (0.81–1.18)	5	10.4	0.48 (0.16–1.12)
Rectal cancer
Total	60	103.3	0.58 (0.44–0.75)	55	67.7	0.81 (0.61–1.06)
Follow-up
⩽3 months	1	1.4	0.72 (0.02–4.03)	17	2.4	7.20 (4.19–11.54)
4–12 months	5	4.3	1.18 (0.38–2.74)	9	7.0	1.29 (0.59–2.45)
2nd and 3rd year	7	11.1	0.63 (0.25–1.30)	7	17.0	0.41 (0.16–0.85)
4th and 5th year	7	10.6	0.66 (0.27–1.37)	12	14.1	0.85 (0.44–1.48)
6th to 10th year	9	23.7	0.38 (0.17–0.72)	6	21.9	0.27 (0.10–0.60)
>10 years	31	52.3	0.59 (0.40–0.84)	4	5.3	0.76 (0.21–1.95)

Abbreviations: CI=confidence interval; SIR=standardised incidence ratio.