Physicians are embedded in informal networks that result from their sharing of patients, information, and behaviors.
To identify professional networks among physicians, examine how such networks vary across geographic regions, and determine factors associated with physician connections.
Design, Setting, and Participants
Using methods adopted from social networkanalysis, Medicare administrative data from 2006 were used to study 4 586 044 Medi-
care beneficiaries seen by 68 288 physicians practicing in 51 hospital referral regions(HRRs). Distinct networks depicting connections between physicians (defined basedon shared patients) were constructed for each of the 51 HRRs.
Main Outcomes Measures
Variation in network characteristics across HRRs and factors associated with physicians being connected.