title: The estimation power of alternative comorbidity indices.
abstract: OBJECTIVE
  Health-care expenditures are strongly influenced by overall illness burden. Appropriate risk adjustment is required for correct policy analysis. We compared three risk adjustment methods: the Charlson comorbidity index (CCI), the chronic disease score (CDS), and the Agency for Healthcare Research and Quality's comorbidity index (AHRQCI) in terms of their estimation power in analyzing health-care expenditures.
  
  
  METHODS
  Data from the Thomson MarketScan Research Databases (Thomson Healthcare, Ann Arbor, MI) were used to estimate total health-care expenditures of migraine patients treated by a triptan. Seven distinct multivariate models were evaluated for model fit (CCI only, CDS only, AHRQCI only, CCI + CDS, CCI + AHRQCI, CDS + AHRQCI, and CCI + CDS + AHRQCI). The estimation power of these indices (alone and in combination) was evaluated using Bayesian and Akaike information criteria, log-likelihood scores, and pseudo R(2) values.
  
  
  RESULTS
  Confirming results from previous studies, when comorbidity indices were considered individually the results were inconclusive. Statistically the best performance was observed in the model that included all three of the comorbidity measures (CCI + CDS + AHRQCI); however, the practical differences in the estimated values were small.
  
  
  CONCLUSIONS
  Low correlation between these comorbidity indices shows that it is possible to have potential risk factors that are not captured in the single comorbidity index. Each comorbidity measure considers different risks, and the collinearity of the three measures is not strong enough to preclude using them simultaneously in the same model.
authors.affiliation: STATinMED Research and University of Michigan, Ann Arbor, MI 48104, USA. obaser@statinmed.com
authors.forename: Onur
authors.initials: O
authors.lastname: Baser
authors.forename: Liisa
authors.initials: L
authors.lastname: Palmer
authors.forename: Judith
authors.initials: J
authors.lastname: Stephenson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002908:Chronic Disease; D015897:Comorbidity; D019992:Databases as Topic; D005260:Female; D017048:Health Care Costs; D006305:Health Status Indicators; D006801:Humans; D007345:Insurance Claim Review; D008297:Male; D008875:Middle Aged; D008881:Migraine Disorders / Q000188:drug therapy* / Q000191:economics / Q000453:epidemiology; D015999:Multivariate Analysis; D012044:Regression Analysis; D012189:Retrospective Studies; D020379:Risk Adjustment / Q000379:methods*; D013223:Statistics as Topic; D014363:Tryptamines / Q000191:economics / Q000627:therapeutic use*; D014481:United States; D055815:Young Adult
chemical_list: D014363:Tryptamines