Table 1.

Characteristics of hospitalizations in training and test sets

	Training data (n = 194,470)		Test data (n = 21,751)
	Hospital A (n = 85,522)	Hospital B (n = 108,948)	Hospital A (n = 9624)	Hospital B (n = 12,127)
Demographics
Age, median (IQR) y	56 (29)	57 (29)	55 (29)	57 (30)
Female sex, no. (%)	46,848 (54.8%)	62,004 (56.9%)	5364 (55.7%)	6935 (57.2%)
Disease cohort, no. (%)
Medical	46,579 (54.5%)	55,087 (50.6%)	5263 (54.7%)	6112 (50.4%)
Cardiovascular	4616 (5.4%)	6903 (6.3%)	528 (5.5%)	749 (6.2%)
Cardiopulmonary	3498 (4.1%)	9028 (8.3%)	388 (4.0%)	1102 (9.1%)
Neurology	6247 (7.3%)	6653 (6.1%)	697 (7.2%)	736 (6.1%)
Cancer	14,544 (17.0%)	19,328 (17.7%)	1617 (16.8%)	2087 (17.2%)
Psychiatry	788 (0.9%)	339 (0.3%)	64 (0.7%)	35 (0.3%)
Obstetrics and newborn	8997 (10.5%)	10,462 (9.6%)	1036 (10.8%)	1184 (9.8%)
Other	253 (0.3%)	1148 (1.1%)	31 (0.3%)	122 (1.0%)
Previous hospitalizations, no. (%)
0 hospitalizations	54,954 (64.3%)	56,197 (51.6%)	6123 (63.6%)	6194 (51.1%)
≥1 and <2 hospitalizations	14,522 (17.0%)	19,807 (18.2%)	1620 (16.8%)	2175 (17.9%)
≥2 and <6 hospitalizations	12,591 (14.7%)	24,009 (22.0%)	1412 (14.7%)	2638 (21.8%)
≥6 hospitalizations	3455 (4.0%)	8935 (8.2%)	469 (4.9%)	1120 (9.2%)
Discharge location no. (%)
Home	70,040 (81.9%)	91,273 (83.8%)	7938 (82.5%)	10,109 (83.4%)
Skilled nursing facility	6601 (7.7%)	5594 (5.1%)	720 (7.5%)	622 (5.1%)
Rehabilitation	2666 (3.1%)	5136 (4.7%)	312 (3.2%)	649 (5.4%)
Another healthcare facility	2189 (2.6%)	2052 (1.9%)	243 (2.5%)	220 (1.8%)
Expired	1816 (2.1%)	2679 (2.5%)	170 (1.8%)	265 (2.2%)
Other	2210 (2.6%)	2214 (2.0%)	241 (2.5%)	262 (2.2%)
Primary outcomes
In-hospital deaths, no. (%)	1816 (2.1%)	2679 (2.5%)	170 (1.8%)	265 (2.2%)
30-day readmissions, no. (%)	9136 (10.7%)	15,932 (14.6%)	1013 (10.5%)	1837 (15.1%)
Hospital stays at least 7 days, no. (%)	20,411 (23.9%)	26,109 (24.0%)	2145 (22.3%)	2931 (24.2%)
No. of ICD-9 diagnoses, median (IQR)	12 (16)	10 (10)	12 (16)	10 (10)