Table 2.

Descriptive Statistics for 2001–2002 Surgeries with and without Patient Safety Events

	No PSI
Variables	Raw Sample	Matched Sample	PSI Raw Sample†
Patient characteristics
In an HMO Plan	0.267	0.218	0.222
Hourly wage worker	0.259	0.342	0.321
Female	0.655	0.518	0.528
Mean age (SD)	44.7 (14.6)	49.6 (13.9)	49.4 (14.0)
Emergency admission	0.122	0.213	0.220
Organ transplant	0.004	0.019	0.011*
Year 2002	0.588	0.614	0.616
Chronic conditions
Congestive heart failure	0.011	0.082	0.074
Valvular disease	0.015	0.046	0.045
Peripheral vascular disease	0.017	0.060	0.055
Hypertension	0.088	0.114	0.117
Paralysis	0.004	0.023	0.023
Other neurological disorders	0.008	0.049	0.049
Chronic pulmonary disease	0.030	0.065	0.062
Diabetes	0.046	0.078	0.079
Diabetic complications	0.009	0.029	0.025
Hypothyroidism	0.015	0.010	0.011
Renal failure	0.011	0.078	0.075
Liver disease	0.006	0.022	0.022
Metastatic cancer	0.018	0.045	0.047
Tumor without metastasis	0.031	0.071	0.069
Rheumatoid arthritis	0.011	0.038	0.040
Obesity	0.013	0.010	0.011
Weight loss	0.003	0.026	0.030
Electrolyte disorders	0.018	0.070	0.067
Deficiency anemias	0.027	0.042	0.051*
Depression/drug abuse	0.013	0.019	0.024
Market characteristics
HMO penetration (SD)	0.204 (0.142)	0.213 (0.144)	0.215 (0.140)
Northeast	0.124	0.124	0.129
North Central	0.301	0.341	0.339
South	0.451	0.434	0.422
West	0.124	0.101	0.110
N	156,864	4,140	4,140

The matched sample consists of all 4,140 PSI events in the raw sample, along with 4,140 non-PSI events matched to the PSI events by propensity score based on the covariates of this table in addition to 92 DRG classes.

^*Outcome rate under the PSI case is significantly different from the rate under the matched non-PSI cases at the 95% level.

^†All rates under PSI cases are significantly different from the rate under the raw sample non-PSI cases at the 95% level, except for obesity.

DRG, diagnosis-related groups; HMO, health maintenance organization; PSI, Patient Safety Indicator; SD, standard deviation.