title: Assessing the outcomes of coronary artery bypass graft surgery: how many risk factors are enough? Steering Committee of the Cardiac Care Network of Ontario.
abstract: OBJECTIVE
  We sought to determine whether more comprehensive risk-adjustment models have a significant impact on hospital risk-adjusted mortality rates after coronary artery bypass graft surgery (CABG) in Ontario, Canada.
  
  
  BACKGROUND
  The Working Group Panel on the Collaborative CABG Database Project has categorized 44 clinical variables into 7 core, 13 level 1 and 24 level 2 variables, to reflect their relative importance in determining short-term mortality after CABG.
  
  
  METHODS
  Using clinical data for all 5,517 patients undergoing isolated CABG in Ontario in 1993, we developed 12 increasingly comprehensive risk-adjustment models using logistic regression analysis of 6 of the Panel's core variables and 6 of the Panel's level 1 variables. We studied how the risk-adjusted mortality rates of the nine cardiac surgery hospitals in Ontario changed as more variables were included in these models.
  
  
  RESULTS
  Incorporating six of the core variables in a risk-adjustment model led to a model with an area under the receiver operating characteristic (ROC) curve of 0.77. The ROC curve area slightly improved to 0.79 with the inclusion of six additional level 1 variables (p = 0.063). Hospital risk-adjusted mortality rates and relative rankings stabilized after adjusting for six core variables. Adding an additional six level 1 variables to a risk-adjustment model had minimal impact on overall results.
  
  
  CONCLUSIONS
  A small number of core variables appear to be sufficient for fairly comparing risk-adjusted mortality rates after CABG across hospitals in Ontario. For efficient interprovider comparisons, risk-adjustment models for CABG could be simplified so that only essential variables are included in these models.
authors.affiliation: Institute for Clinical Evaluative Sciences in Ontario, Sunnybrook Health Science Centre, North York, Canada. tu@ices.on.ca
authors.forename: J V
authors.initials: JV
authors.lastname: Tu
authors.forename: K
authors.initials: K
authors.lastname: Sykora
authors.forename: C D
authors.initials: CD
authors.lastname: Naylor
mesh_terms: D000368:Aged; D001026:Coronary Artery Bypass / Q000401:mortality*; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D017063:Outcome Assessment, Health Care / Q000379:methods*; D012372:ROC Curve; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors