title: The impact of hospital mergers on treatment intensity and health outcomes.
abstract: OBJECTIVE
  To analyze the impact of hospital mergers on treatment intensity and health outcomes.
  
  
  METHODS
  Hospital inpatient data from California for 1990 through 2006, encompassing 40 mergers.
  
  
  METHODS
  I used a geographic-based IV approach to determine the effect of a zip code's exposure to a merger. The merged facility's market share represents exposure, instrumented with combined premerge shares. Additional specifications include Herfindahl Index (HHI), instrumented with predicted change in HHI.
  
  
  RESULTS
  The primary specification results indicate that merger completion is associated with a 3.7 percent increase in the utilization of bypass surgery and angioplasty and a 1.7 percent increase in inpatient mortality above averages in 2000 for the average zip code. Isolating the competition mechanism mutes the treatment intensity result slightly, but it more than doubles the merger exposure effect on inpatient mortality to a 3.9 percent increase. The competition mechanism is associated with a sizeable increase in number of procedures.
  
  
  CONCLUSIONS
  Unlike previous studies, this analysis finds that hospital mergers are associated with increased treatment intensity and higher inpatient mortality rates among heart disease patients. Access to additional outcome measures such as 30-day mortality and readmission rates might shed additional light on whether the relationship between these outcomes is causal.
authors.affiliation: Congressional Budget Office, Ford House Office Building, Fourth Floor,Washington,DC 20515, USA. tamara.hayford@cbo.gov
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Hayford
mesh_terms: D000368:Aged; D002140:California; D006348:Cardiac Surgical Procedures / Q000706:statistics & numerical data*; D004465:Economic Competition; D005260:Female; D006273:Health Facility Merger; D017052:Hospital Mortality; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000401:mortality / Q000628:therapy*; D017063:Outcome Assessment, Health Care; D020379:Risk Adjustment; D017062:Small-Area Analysis
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