title: Look back for the Charlson Index did not improve risk adjustment of cancer surgical outcomes.
abstract: OBJECTIVE
  The Charlson score is a commonly used measure of comorbidity; however, there is little empirical research into the optimal implementation when studying cancer surgery outcomes using administrative data. We compared four alternative Charlson score implementations, including and excluding metastatic cancer and varying the look-back periods.
  
  
  METHODS
  Nine years of linked administrative data were used to identify patients undergoing surgery for cancer of the colon, rectum, or lung in New South Wales, Australia. Four binary outcomes of 30- and 365-day mortality, length of stay greater than 21 days, and emergency readmission within 28 days were compared between groups of similar hospitals. Hospital risk adjustment models were compared for alternative Charlson score implementations.
  
  
  RESULTS
  Excluding metastatic cancer from the Charlson score improved model performance for short-term outcomes, but there was no implementation that was consistently optimal. Incorporating a look-back period reduced the number of patients for analysis but did not improve hospital risk adjustment.
  
  
  CONCLUSIONS
  Charlson scores for hospital risk adjustment of short-term outcomes of cancer surgery should be calculated excluding metastatic cancer as a separate comorbidity. We found no clear best performing implementation and found no benefit in incorporating any look-back period.
authors.affiliation: National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology and Environment, The Australian National University, Building 62, Mills Road, Canberra ACT 0200, Australia.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Dobbins
authors.affiliation: Cancer Institute NSW, Level 9, 8 Central Avenue, Eveleigh, NSW 2015, Australia.
authors.forename: Nicola
authors.initials: N
authors.lastname: Creighton
authors.affiliation: Cancer Institute NSW, Level 9, 8 Central Avenue, Eveleigh, NSW 2015, Australia.
authors.forename: David C
authors.initials: DC
authors.lastname: Currow
authors.affiliation: Sydney School of Public Health, Level 6, Lifehouse at RPAH (C39Z), University of Sydney NSW 2006, Australia. Electronic address: jane.young@sydney.edu.au.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Young
mesh_terms: D001315:Australia / Q000453:epidemiology; D015897:Comorbidity; D005260:Female; D006761:Hospitals; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000401:mortality / Q000601:surgery*; D009517:New South Wales / Q000453:epidemiology; D017063:Outcome Assessment, Health Care; D011379:Prognosis; D012107:Research Design; D020379:Risk Adjustment; D012720:Severity of Illness Index; D016896:Treatment Outcome
keywords: Administrative data; Cancer; Comorbidity; Hospital readmission; Mortality; Risk adjustment