Table 1. Patient and Hospital Characteristics at the Time of the Index Operation^a.

Characteristic	All Patients	Patients Without Reoperation	Patients Undergoing Reoperation	P Value Without Reoperation vs Undergoing Reoperation
No. of patients	25 042	20 406	4636	NA
Age, mean, y	57.56	57.51	57.75	.22
Men, %	27.55	28.42	23.75	<.001
White, %	82.61	82.92	81.22	.01
Comorbidities, %b
Hypertension	71.78	73.35	64.88	<.001
Diabetes	43.83	44.61	40.38	<.001
Depression	21.78	21.81	21.68	.85
Chronic pulmonary disease	23.23	23.18	23.47	.67
Hypothyroidism	13.50	13.33	14.24	.11
Liver disease	6.59	7.05	4.57	<.001
Psychoses	5.22	4.90	6.62	<.001
Deficiency anemias	2.89	2.38	5.11	<.001
Renal failure	4.29	4.25	4.44	.57
Fluid and electrolyte disorders	3.33	2.18	8.43	<.001
Congestive heart failure	5.24	5.24	5.22	.95
Rheumatoid arthritis	2.58	2.61	2.44	.49
Valvular disease	1.88	1.86	2.01	.51
Peripheral vascular disease	1.41	1.38	1.55	.39
Coagulopathy	0.46	0.38	0.82	.00
Paralysis	0.47	0.46	0.52	.62
Elixhauser No. of comorbidities, %
0	5.83	5.52	7.20	<.001
1	20.83	21.49	17.95	<.001
≥2	73.33	72.99	74.85	.01
No. of hospitals	732	631	564	NA
Ownership, %
For-profit	24.37	22.01	34.64	<.001
Nonprofit	66.37	68.59	56.73	<.001
Other	9.26	9.40	8.63	.09
Bed size, %
<250 beds	29.02	29.83	26.24	<.001
>250 to <500 beds	43.19	41.45	49.13	<.001
>500 beds	28.31	29.24	24.23	<.001
Geographic region, %
Northeast	17.91	18.47	15.47	<.001
Midwest	22.57	23.37	19.13	<.001
South	42.86	41.03	50.84	<.001
West	16.65	17.13	14.56	<.001
Teaching hospital, %	60.23	61.72	54.44	<.001
No. of operating rooms	22.78	22.66	23.27	.08
Nurse ratio	7.13	7.10	7.28	.01

Abbreviation: NA, not applicable.

^aData source: Medicare claims, 2006 to 2013, and the American Hospital Association Annual Survey.

^bComorbid diseases as defined by the Healthcare Cost and Utilization Project. Full definitions of the codes used can be found here: https://www.hcup-us.ahrq.gov/toolssoftware/comorbidity/comorbidity.jsp.