Table 1. Summaries and the corresponding p-values before and after using nearest neighbor propensity score matching.

The means and standard deviations of each of the two groups are provided for age and length of stay, while frequencies and proportions are provided for gender, race, ethnicity, diagnostic group, and severity index (n = 2,387 for the unmatched sample; n = 735 for the matched sample).

	Unmatched Sample (n=2387)			Matched Sample (n=735)
Covariate	Readmitted (n=245)	Not readmitted (n=2142)	P-Values	Readmitted (n=245)	Not Readmitted (n=490)	P-Values
Age (mean, sd)	67.6 (12.2)	66.4 (13.2)	0.1529	67.6 (12.2)	68.4 (13.4)	0.4211
Length of stay (mean, sd)	4.5 (4.6)	5.2 (8.7)	0.0721	4.4 (4.6)	4.5 (4.3)	0.5928
Diagnostic group			0.0019			0.9848
Cardiovascular	64 (26%)	734 (34%)		64 (26%)	118 (24%)
Gastrointestinal	34 (14%)	236 (11%)		34 (14%)	76 (16%)
Infections	31 (13%)	206 (10%)		31 (13%)	64 (13%)
Metabolic	22 (9%)	157 (7%)		22 (9%)	54 (11%)
Neurological	9 (4%)	201 (9%)		9 (4%)	17 (3%)
Renal	17 (7%)	90 (4%)		17 (7%)	31 (6%)
Respiratory	40 (16%)	287 (13%)		40 (16%)	76 (16%)
Other	29 (11%)	231 (11%)		29 (11%)	54 (11%)
Ethnicity			0.5718			0.7254
Hispanic	2 (1%)	31 (2%)		2 (1%)	6 (2%)
Not Hispanic	243 (99%)	2,111 (98%)		243 (99%)	484 (98%)
Gender			0.2051			0.1663
Female	6 (3%)	94 (4%)		6 (3%)	24 (3%)
Male	239 (97%)	2,048 (96%)		239 (97%)	466 (97%)
Race			0.6422			0.2573
White	129 (53%)	1,193 (56%)		129 (53%)	289 (59%)
Black	113 (46%)	923 (43%)		113 (46%)	196 (40%)
Other	3 (1%)	26 (1%)		3 (1%)	5 (1%)
Severity Index			<0.0001			0.205
<2.5%	127 (52%)	1,468 (69%)		127 (52%)	272 (56%)
2.5 - 5%	63 (26%)	314 (15%)		63 (26%)	143 (29%)
5 - 10%	30 (12%)	213 (10%)		30 (12%)	39 (8%)
10 - 30%	22 (9%)	108 (5%)		22 (9%)	32 (7%)
>=30%	3 (1%)	39 (1%)		3 (1%)	4 (<1%)