Table 1.

Sample Characteristics and Balance

			Standardized Difference
	Mean	Standard Deviation	1(Instrument > Median)
Age	81.614	7.596	−0.029
Male	0.376	0.484	−0.002
Race: Black	0.073	0.264	0.017
Race: Other	0.031	0.174	0.006
Hypertension	0.409	0.490	−0.028
Stroke	0.068	0.253	0.004
Cerebrovascular Disease	0.101	0.300	−0.004
Renal Failure Disease	0.155	0.353	−0.053
Dialysis	0.015	0.122	−0.001
COPD	0.212	0.408	−0.008
Pneumonia	0.191	0.391	−0.015
Diabetes	0.196	0.396	−0.009
Protein Calorie Malnutrition	0.070	0.252	−0.014
Dementia	0.176	0.381	0.000
Paralysis	0.085	0.278	−0.002
Peripheral Vascular Disease	0.131	0.336	−0.010
Metastatic Cancer	0.034	0.181	0.000
Trauma	0.137	0.342	−0.012
Substance Abuse	0.067	0.247	−0.014
Major Psych. Disorder	0.056	0.229	−0.004
Chronic Liver Disease	0.010	0.097	0.000
Ambulance: Miles Traveled with Patient	7.051	8.216	0.006
Ambulance: Advanced Life Support	0.688	0.467	−0.041
Ambulance: Emergency Transport	0.912	0.293	−0.048
Ambulance: Outpatient File	0.072	0.242	−0.074
Ambulance: Payment	340.510	192.316	−0.108

Notes: N=1,575,273. Balance statistics report the standardized difference based on the difference in the mean of the covariate when the instrument is above versus below its median value computed from a regression model that controls for year and ZIP code × patient origin fixed effects, divided by the pooled standard deviation. Average age reported here, however in all regression models age controls are included as dummy variables for 5 year age bins starting at age 66.

Source: 2002–2012 Medicare Part A and B Data