Referral paths in the U.S. physician network

Applied Network Science

Table 2 Some national referral network measures in 2006-2011

Year	2006	2007	2008	2009	2010	2011
# nodes	272353	296008	313051	323042	334452	347586
# edges	5708791	5948185	6313136	6544847	6785594	7047586
Exponent of indegree power law	3.08	2.80	1.55	2.76	1.54	2.74
p-value of indegree power law test	0.97	0.89	0.21	0.85	0.22	0.82
Exponent of outdegree power law	3.01	2.69	2.71	2.66	2.56	2.68
p-value of outdegree power law test	0.9	0.94	0.93	0.96	0.91	0.93
Size of the largest connected component	271898	295405	312412	322452	333727	346711
(in, in) degree assortativity	-0.094	-0.088	-0.084	-0.085	-0.083	-0.084
Self in/out degree correlation	0.983	0.982	0.983	0.983	0.983	0.984
Reciprocity of #referral	0.878	0.890	0.896	0.901	0.902	0.896