title: A new Elixhauser-based comorbidity summary measure to predict in-hospital mortality.
abstract: BACKGROUND
  Recently, van Walraven developed a weighted summary score (VW) based on the 30 comorbidities from the Elixhauser comorbidity system. One of the 30 comorbidities, cardiac arrhythmia, is currently excluded as a comorbidity indicator in administrative datasets such as the Nationwide Inpatient Sample (NIS), prompting us to examine the validity of the VW score and its use in the NIS.
  
  
  METHODS
  Using data from the 2009 Maryland State Inpatient Database, we derived weighted summary scores to predict in-hospital mortality based on the full (30) and reduced (29) set of comorbidities and compared model performance of these and other comorbidity summaries in 2009 NIS data.
  
  
  RESULTS
  Weights of our derived scores were not sensitive to the exclusion of cardiac arrhythmia. When applied to NIS data, models containing derived summary scores performed nearly identically (c statistics for 30 and 29 variable-derived summary scores: 0.804 and 0.802, respectively) to the model using all 29 comorbidity indicators (c=0.809), and slightly better than the VW score (c=0.793). Each of these models performed substantially better than those based on a simple count of Elixhauser comorbidities (c=0.745) or a categorized count (0, 1, 2, or ≥ 3 comorbidities; c=0.737).
  
  
  CONCLUSIONS
  The VW score and our derived scores are valid in the NIS and are statistically superior to summaries using simple comorbidity counts. Researchers wishing to summarize the Elixhauser comorbidities with a single value should use the VW score or those derived in this study.
authors.affiliation: *Department of Quantitative Health Sciences †Neurological Institute Center for Outcomes Research and Evaluation ‡Department of Outcomes Research §Neurological Institute ∥Epilepsy Center ¶Department of Neurosurgery, Cleveland Clinic, Cleveland, OH #Department of Neurosurgery, University of California, Irvine, Orange, CA.
authors.forename: Nicolas R
authors.initials: NR
authors.lastname: Thompson
authors.forename: Youran
authors.initials: Y
authors.lastname: Fan
authors.forename: Jarrod E
authors.initials: JE
authors.lastname: Dalton
authors.forename: Lara
authors.initials: L
authors.lastname: Jehi
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Rosenbaum
authors.forename: Sumeet
authors.initials: S
authors.lastname: Vadera
authors.forename: Sandra D
authors.initials: SD
authors.lastname: Griffith
mesh_terms: D015897:Comorbidity; D006305:Health Status Indicators; D017052:Hospital Mortality; D006801:Humans; D007297:Inpatients; D008396:Maryland