title: A multipurpose comorbidity scoring system performed better than the Charlson index.
abstract: OBJECTIVE
  To develop a comorbidity scoring system that out-performs the Charlson index.
  
  
  METHODS
  Population-based cohorts of medical (n=326,456), procedural (n=349,686), and psychiatric (n=16,895) inpatients in Western Australia were followed for 1-year mortality, 30-day readmissions, and length of stay (LOS) using data linkage. Conditions were identified at index admission and over the preceding 12 months. A Multipurpose Australian Comorbidity Scoring System (MACSS) was developed, based on the most frequent 102 comorbid conditions associated with a rate ratio (RR) > or = 1.1 of death or readmission or a LOS difference > or =0.5 days. The performance of MACSS and the Charlson index in predicting mortality, readmission, and LOS, and in controlling confounding by comorbidity, was compared in five test scenarios involving asthma, myocardial infarction, mastectomy, transurethral prostatectomy, and major depressive illness.
  
  
  RESULTS
  MACSS performed better than the Charlson index on all three outcomes in all five clinical groups. It reduced the failure of the Charlson index to discriminate on mortality and readmission outcomes by 5-40%, improved R(2) in LOS models by up to fourfold and often doubled the correction of originally confounded effect measures.
  
  
  CONCLUSIONS
  The use of the MACSS and similar alternatives to the Charlson index are a new methodologic standard for adjustment of comorbidity risk.
authors.affiliation: Centre for Health Services Research, School of Population Health, The University of Western Australia, 35 Stirling Highway, MDP M431, Crawley 6009, Australia. darch@dph.uwa.edu.au
authors.forename: C D'Arcy J
authors.initials: CD
authors.lastname: Holman
authors.forename: David B
authors.initials: DB
authors.lastname: Preen
authors.forename: Natalya J
authors.initials: NJ
authors.lastname: Baynham
authors.forename: Judith C
authors.initials: JC
authors.lastname: Finn
authors.forename: James B
authors.initials: JB
authors.lastname: Semmens
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015897:Comorbidity; D005260:Female; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data; D008297:Male; D008498:Medical Record Linkage; D008875:Middle Aged; D009026:Mortality; D017063:Outcome Assessment, Health Care / Q000379:methods; D010359:Patient Readmission / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D020379:Risk Adjustment / Q000379:methods; D012720:Severity of Illness Index; D014904:Western Australia / Q000453:epidemiology