Variation in Patient-Sharing Networks of Physicians Across the United States

Context

Physicians are embedded in informal networks that result from their sharing of patients, information, and behaviors.

Objectives

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.

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