Medical Practice Consolidation and Physician Shared Patient Network Size, Strength, and Stability

Published in: Medical Care, Volume 57, Issue 9, pages 680-687 (September 2019). doi: 10.1097/MLR.0000000000001168

Posted on on August 20, 2019

by Claire E. O'Hanlon, Christopher M. Whaley, Deborah Anne Freund

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Properties of social networks and shared patient networks of physicians are associated with important outcomes, including costs, quality, information exchange, and organizational effectiveness.


To determine whether practice consolidation affects size, strength, and stability of US practice-based physician shared patient networks.

Research Design

We used a dynamic difference-in-differences (event study) design to determine how 2 types of vertical consolidation (hospital and health system practice acquisition) and 2 types of horizontal consolidation (medical group membership and practice-practice mergers) affect individual shared patient network characteristics, controlling for physician fixed effects and geographic market (metropolitan statistical area).


Practice-based US physicians whose practices consolidated 2009-2014 are identified via health system, hospital, and medical group affiliation information and appearance/disappearance of listed practice affiliations in the SK&A Physician Database.


Outcomes measured were network size (number of individual physicians with whom a physician shares patients within 30-d), strength (average number of shared patients within those relationships), and stability (percent of shared patient relationships that persist in the current and prior year), all generated from Medicare Shared Patient Patterns (30-d) data.


Shared patient network stability increases significantly after acquisition of practices by horizontal practice-practice mergers [[beta]t=1=0.041 (P<0.001), [beta]t=2=0.047 (P<0.001), [beta]t=3=0.041 (P<0.001), [beta]t=4=0.031 (P<0.05), where t is the number of years after the consolidation event]. These effects were robust to sensitivity analyses. Shared patient network size and strength are not observably associated with practice consolidation events.


Practice consolidation can increase the stability of physician networks, which may have positive implications for organizational effectiveness.

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