Table 1.

Description of Physicians, Their Medicare Beneficiaries, and Network Characteristics stratified by HRR

	Mean (SD)	Range		Example HRRs
		Min	Max	Boston, MA	Minot, ND	Joliet, IL	Miami, FL
Number of Physicians(nodes)	1,339	93	8,197	8,197	135	496	3,600
Physician Characteristics
Mean Age	48.5 (1.3)	46.1	51.7	48.3	48.0	46.3	51.7
Percent Male	80.3 (4.9)	69.2	89.7	70.1	82.4	77.8	84.1
% Primary Care	41.9 (5.4)	27.6	53.3	38.5	50.4	40.1	39.0
% Medical Specialists	30.0 (4.8)	20.7	47.0	36.8	20.7	33.5	35.7
% Surgical Specialists	28.0 (3.3)	21.3	35.5	24.7	28.9	26.3	25.2
Patient Population Characteristics
White (% of population)	86.6(11.5)	49.4	98.8	89.1	92.7	89.3	61.7
Black (% of population)	8.9 (10.1)	0.1	42.1	6.2	0.2	8.8	111.9
Hispanic (% of population)	1.8 (4.0)	0.0	24.2	1.5	0.0	1.0	24.2
Female (% of population)	59.9(2.0)	54.4	64.2	60.8	58.0	61.5	61.1
Medicaid(% of population)	23.0 (10.0)	7.7	51.9	27.7	12.0	14.8	51.9
Age (mean)	70.7 (1.6)	67.1	74.6	70.8	73.2	71.4	71.6
HCC Score (mean)	1.9 (.3)	1.5	2.8	2.2	1.7	2.0	2.8
ETG intensity Score (mean)	1.03 (.06)	0.9	1.2	1.1	1.2	1.0	1.1
# of patients (mean)	279 (84)	126	447	224	260	316	228
Network Characteristics
Number of ties	50,927 (75,962)	1,568	392,582	392,582	1,568	12,914	218,136
Adjusted Degree	27.3 (10.4)	11.7	54.4	51.4	11.7	18.6	54.4
Number of Shared Patients	852 (336)	297	1,503	835	498	1222	1146
Clustering	.55 (.06)	.40	.67	.48	.67	.62	.47
PCP Relative Centrality	.38 (.17)	.19	1.06	.52	.41	.19	.46
Medical Specialist	3.47 (1.33)	.47	7.40	1.62	5.59	3.98	2.12
Relative Centrality

HCC is hierarchical clinical conditions, ETG is Episode Treatment Group, HRR is hospital referral region. Thresholds refers to the mean number of shared patients required for establishing a tie in the respective HRRs. The SD is the standard deviation of the means.