Patient-Sharing Networks of Physicians and Health Care Utilization and Spending Among Medicare Beneficiaries

IMPORTANCE: Physicians are embedded in informal networks in which they share patients, information, and behaviors. OBJECTIVE: We examined the association between physician network properties and health care spending, utilization, and quality of care among Medicare beneficiaries. DESIGN, SETTING, AND PARTICIPANTS: In this cross-sectional study, we applied methods from social network analysis to Medicare administrative data from 2006 to 2010 for an average of 3 761 223 Medicare beneficiaries per year seen by 40 241 physicians practicing in 51 hospital referral regions (HRRs) to identify networks of physicians linked by shared patients. We improved on prior methods by restricting links to physicians who shared patients for distinct episodes of care, thereby excluding potentially spurious linkages between physicians treating common patients but for unrelated reasons. We also identified naturally occurring communities of more tightly linked physicians in each region. We examined the relationship between network properties measured in the prior year and outcomes in the subsequent year using regression models. MAIN OUTCOMES AND MEASURES: Spending on total medical services, hospital, physician, and other services, use of services, and quality of care. RESULTS: The mean patient age across the 5 years of study was 72.3 years and 58.5% of the participants were women. The mean age across communities of included physicians was 49 years and approximately 78% were men. Mean total annual spending per patient was $10 051. Total spending was higher for patients of physicians with more connections to other physicians ($1009 for a 1–standard deviation increase, P