Table 1

Characteristics of the 24 240 hospital spells, stratified by cases and controls. In addition, the frequency and percentage of patients across the categories of covariates used in the multivariable regression are given, with corresponding χ² tests for significance (see online supplemental material for full table)

Characteristic	All spells (n=24 240)		Controls (n=21 363)		Cases (n=2877)		P value
Characteristic	n	%	n	%	n	%	P value
Gender
Male	12 032	49.64	10 592	49.58	1440	50.05	0.635
Female	12 208	50.36	10 771	50.42	1437	49.95
Age
Median, IQR	79	72–86	79	72–85	79	73–86
65–70	4740	19.55	4248	19.88	492	17.10	0.004
71–75	4155	17.14	3666	17.16	489	17.00
76–80	4723	19.48	4144	19.4	579	20.13
81–85	4516	18.63	3977	18.62	539	18.73
86+	6106	25.19	5328	24.94	778	27.04
Attended ICU
No	23 642	97.53	20 958	98.1	2684	93.29	<0.001
Yes	598	2.47	405	1.90	193	6.71
Elixhauser comorbidities
Mean, SD	3.54	1.9	3.48	1.89	4.00	1.98
0	695	2.87	651	3.05	44	1.53	<0.001
1–3	12 265	50.6	11 061	51.78	1204	41.85
4–6	9516	39.26	8204	38.4	1312	45.6
7–9	1685	6.95	1386	6.49	299	10.39
10 or more	79	0.33	61	0.29	18	0.63
Time at risk (days)
Median, IQR	6.30	3.61–11.74	6.31	3.60–11.72	6.21	3.69–11.85
2–5	9756	40.25	8610	40.3	1146	39.83	0.016
5–7	3614	14.91	3154	14.76	460	15.99
7–10	3501	14.44	3115	14.58	386	13.42
10–15	3270	13.49	2890	13.53	380	13.21
15–20	1634	6.74	1433	6.71	201	6.99
20–30	1480	6.11	1275	5.97	205	7.13
30–40	611	2.52	541	2.53	70	2.43
40+	374	1.54	345	1.61	29	1.01
Procedures
Median, IQR	2	0–5	2	0–5	2	0–5
Procedures (n)	7866	32.45	7057	33.03	809	28.12	<0.001
1	1854	7.65	1451	6.79	403	14.01
2–8	11 917	49.16	10 531	49.3	1386	48.18
9–13	1837	7.58	1659	7.77	178	6.19
14 or more	766	3.16	665	3.11	101	3.51
Hospital site of admission
1	7704	31.78	6831	31.98	873	30.34	<0.001
2	12 348	50.94	10 940	51.21	1408	48.94
3	4188	17.28	3592	16.81	596	20.72

ICU, intensive care unit; IQR, Interquartile range .