title: A Simple Method for Evaluating Within Sample Prognostic Balance Achieved by Published Comorbidity Summary Measures.
abstract: OBJECTIVE
  To demonstrate how a researcher can investigate the appropriateness of a published comorbidity summary measure for use with a given sample.
  
  
  METHODS
  Surveillance, Epidemiology, and End Results linked to Medicare claims data.
  
  
  METHODS
  We examined Kaplan-Meier estimated survival curves for four diseases within strata of a comorbidity summary measure, the Charlson Comorbidity Index.
  
  
  METHODS
  We identified individuals with early-stage kidney cancer diagnosed from 1995 to 2009. We recorded comorbidities present in the year before diagnosis.
  
  
  RESULTS
  The use of many comorbidity summary measures is valid under appropriate conditions. One condition is that the relationships of the comorbidities with the outcome of interest in a researcher's own population are comparable to the relationships in a published algorithm's population. The original comorbidity weights from the Charlson Comorbidity Index seemed adequate for three of the diseases in our sample. We found evidence that the Charlson Comorbidity Index might underestimate the impact of one disease in our sample.
  
  
  CONCLUSIONS
  Examination of survival curves within strata defined by a comorbidity summary measure can be a useful tool for determining whether a published method appropriately accounts for comorbidities. A comorbidity score is only as good as those variables included.
authors.affiliation: Biostatistics and Bioinformatics Facility, Fox Chase Cancer Center, Temple University Health System, 333 Cottman Avenue, Philadelphia, PA, 19111.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Egleston
authors.affiliation: Department of Surgery, Fox Chase Cancer Center, Temple University Health System, Philadelphia, PA.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Uzzo
authors.affiliation: Office of Academic Affairs, Fox Chase Cancer Center, Temple University Health System, Philadelphia, PA.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Beck
authors.affiliation: Medical Oncology, Fox Chase Cancer Center, Temple University Health System, Philadelphia, PA.
authors.forename: Yu-Ning
authors.initials: YN
authors.lastname: Wong
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D053208:Kaplan-Meier Estimate; D007680:Kidney Neoplasms / Q000175:diagnosis* / Q000453:epidemiology* / Q000401:mortality; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D011379:Prognosis; D018426:SEER Program / Q000706:statistics & numerical data; D012737:Sex Factors; D012959:Socioeconomic Factors; D014481:United States
keywords: Comorbidity scores; SEER-Medicare; diagnostics; prognostic balance; prognostic scores