Table 2

Standardised incidence ratios (SIRS) and 95% confidence intervals (CI) for pancreatic cancer among patients who had a cholecystectomy for cholelithiasis, by duration of follow up, age at entry, and calendar year at entry

	Total					Without diabetes/chronic pancreatitis
	Obs^2-151	SIR	95% CI	Obs^2-151	SIR	95% CI	Obs^2-151	SIR	95% CI
Duration of follow up (y)
<1	231	4.72	4.13–5.37	0	—	—	231	4.95	4.33–5.63
1	92	1.91	1.54–2.34	9	3.84	1.76–7.29	83	1.81	1.44–2.25
2–32	730	1.06	0.98–1.14	72	1.85	1.44–2.32	658	1.01	0.94–1.09
2–4	151	1.10	0.93–1.29	11	1.58	0.79–2.82	140	1.07	0.90–1.27
5–9	210	1.06	0.93–1.22	21	1.96	1.21–2.99	189	1.01	0.87–1.17
10–14	165	1.07	0.91–1.25	12	1.34	0.69–2.34	153	1.05	0.89–1.23
15–19	115	1.05	0.87–1.26	12	1.83	0.94–3.19	103	1.00	0.82–1.21
20–32	89	0.98	0.79–1.20	16	2.78	1.59–4.51	73	0.86	0.67–1.08
p value for trend^2-152		0.44			0.24			0.19
Calendar year at entry^2-153
1965–74	352	1.10	0.99–1.22	39	2.36	1.68–3.23	313	1.03	0.92–1.15
1975–84	266	0.98	0.86–1.10	25	1.53	0.99–2.25	241	0.94	0.83–1.07
1985–97	112	1.16	0.96–1.40	8	1.31	0.56–2.58	104	1.15	0.94–1.40
p value for trend		0.91			0.05			0.67
Age at entry (y)^2-153
<40	48	1.33	0.98–1.77	7	7.36	2.96–15.2	41	1.17	0.84–1.59
40–49	95	1.07	0.86–1.30	9	2.76	1.26–5.24	86	1.00	0.80–1.24
50–59	197	1.02	0.88–1.17	18	1.92	1.14–3.04	179	0.98	0.84–1.13
60–69	247	1.07	0.94–1.21	20	1.38	0.84–2.12	227	1.05	0.92–1.19
⩾70	143	1.02	0.86–1.20	18	1.65	0.98–2.61	125	0.96	0.80–1.15
p value for trend		0.31			<0.01			0.60
Diabetes^2-153
No	664	1.02	0.94–1.10
Yes	66	1.79	1.39–2.28
Chronic pancreatitis^2-153
No	722	1.04	0.97–1.12
Yes	8	3.17	1.37–6.24

↵2-150 Person time before the onset of comorbidities was attributed to the comorbidity negative strata.
↵2-151 Observed number of pancreatic cancer cases.
↵2-152 The category of 2–4 years after index surgery was taken as the reference.
↵2-153 The first two years of observation were not included in the analyses.