title: Correlations among risk-standardized mortality rates and among risk-standardized readmission rates within hospitals.
abstract: BACKGROUND
  Hospital-level, 30-day risk-standardized mortality and readmission rates are publicly reported for Medicare patients admitted with acute myocardial infarction (AMI), heart failure (HF), and pneumonia, but the correlations among mortality rates and among readmission rates within US hospitals for these conditions are unknown. Correlation among measures within the same hospital would suggest that there are common hospital-wide quality factors.
  
  
  METHODS
  We designed a cross-sectional study of US hospital 30-day risk-standardized mortality and readmission rates for Medicare fee-for-service beneficiaries from July 2007 to June 2009. We assessed the correlation between pairs of risk-standardized mortality rates and pairs of risk-standardized readmission rates for AMI, HF, and pneumonia.
  
  
  RESULTS
  The mortality cohort included 4559 hospitals, and the readmission cohort included 4468 hospitals. Every mortality measure was significantly correlated with every other mortality measure (range of correlation coefficients, 0.27-0.41, P < 0.0001 for all correlations). Every readmission measure was significantly correlated with every other readmission measure (range of correlation coefficients, 0.32-0.47, P < 0.0001 for all correlations). For each condition pair and outcome, one-third or more of hospitals were in the same quartile of performance. Correlations were highest within large, nonprofit, urban, and/or Council of Teaching Hospitals members. For any given condition pair, the correlation between readmission rates was significantly higher than the correlation between mortality rates (P < 0.01 for all pairs).
  
  
  CONCLUSIONS
  Risk-standardized readmission rates are moderately correlated with each other within hospitals, as are risk-standardized mortality rates. This suggests that there may be common hospital-wide factors affecting hospital outcomes.
authors.affiliation: Center for Outcomes Research and Evaluation, Yale-New Haven Health System, New Haven, CT, USA. leora.horwitz@yale.edu
authors.forename: Leora I
authors.initials: LI
authors.lastname: Horwitz
authors.forename: Yongfei
authors.initials: Y
authors.lastname: Wang
authors.forename: Mayur M
authors.initials: MM
authors.lastname: Desai
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Curry
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Bradley
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Drye
authors.forename: Harlan M
authors.initials: HM
authors.lastname: Krumholz
mesh_terms: D003430:Cross-Sectional Studies; D006333:Heart Failure / Q000401:mortality*; D006739:Hospital Administration / Q000706:statistics & numerical data; D006742:Hospital Bed Capacity / Q000706:statistics & numerical data; D017052:Hospital Mortality; D006801:Humans; D009203:Myocardial Infarction / Q000401:mortality*; D010067:Ownership / Q000706:statistics & numerical data; D010359:Patient Readmission / Q000706:statistics & numerical data*; D011014:Pneumonia / Q000401:mortality*; D012111:Residence Characteristics / Q000706:statistics & numerical data; D020379:Risk Adjustment; D014481:United States / Q000453:epidemiology