title: Do hospital service areas and hospital referral regions define discrete health care populations?
abstract: BACKGROUND
  Effective measurement of health care quality, access, and cost for populations requires an accountable geographic unit. Although Hospital Service Areas (HSAs) and Hospital Referral Regions (HRRs) have been extensively used in health services research, it is unknown whether these units accurately describe patterns of hospital use for patients living within them.
  
  
  OBJECTIVE
  To evaluate the ability of HSAs, HRRs, and counties to define discrete health care populations.
  
  
  METHODS
  Cross-sectional geographic analysis of hospital admissions.
  
  
  METHODS
  All hospital admissions during the year 2011 in Washington, Arizona, and Florida.
  
  
  METHODS
  The main outcomes of interest were 3 metrics that describe patient movement across HSA, HRR, and county boundaries: localization index, market share index, and net patient flow. Regression models tested the association of these metrics with different HSA characteristics.
  
  
  RESULTS
  For 45% of HSAs, fewer than half of the patients were admitted to hospitals located in their HSA of residence. For 16% of HSAs, more than half of the treated patients lived elsewhere. There was an equivalent degree of movement across county boundaries but less movement across HRR boundaries. Patients living in populous, urban HSAs with multiple, large, and teaching hospitals tended to remain for inpatient care. Patients admitted through the emergency department tended to receive care at local hospitals relative to other patients.
  
  
  CONCLUSIONS
  HSAs and HRRs are geographic units commonly used in health services research yet vary in their ability to describe where patients receive hospital care. Geographic models may need to account for differences between emergent and nonemergent care.
authors.affiliation: *Department of Emergency Medicine, Highland Hospital, Oakland CA †Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine ‡Department of Emergency Medicine, Perelman School of Medicine, University of Pennsylvania §Department of Emergency Medicine, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA ∥Department of Health & Human Services, Emergency Care Coordination Center, Office of the Assistant Secretary for Preparedness & Response, Washington, DC.
authors.forename: Austin S
authors.initials: AS
authors.lastname: Kilaru
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Wiebe
authors.forename: David N
authors.initials: DN
authors.lastname: Karp
authors.forename: Jennifer
authors.initials: J
authors.lastname: Love
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kallan
authors.forename: Brendan G
authors.initials: BG
authors.lastname: Carr
mesh_terms: D002391:Catchment Area, Health / Q000706:statistics & numerical data*; D003430:Cross-Sectional Studies; D004467:Economics; D006302:Health Services Research / Q000379:methods*; D006739:Hospital Administration / Q000706:statistics & numerical data*; D006801:Humans; D016014:Linear Models; D012017:Referral and Consultation / Q000706:statistics & numerical data*; D012111:Residence Characteristics