title: Accuracy, calibration and clinical performance of the EuroSCORE: can we reduce the number of variables?
abstract: BACKGROUND
  The European system for cardiac operative risk evaluation (EuroSCORE) is currently used in many institutions and is considered a reference tool in many countries. We hypothesised that too many variables were included in the EuroSCORE using limited patient series. We tested different models using a limited number of variables.
  
  
  METHODS
  A total of 11150 adult patients undergoing cardiac operations at our institution (2001-2007) were retrospectively analysed. The 17 risk factors composing the EuroSCORE were separately analysed and ranked for accuracy of prediction of hospital mortality. Seventeen models were created by progressively including one factor at a time. The models were compared for accuracy with a receiver operating characteristics (ROC) analysis and area under the curve (AUC) evaluation. Calibration was tested with Hosmer-Lemeshow statistics. Clinical performance was assessed by comparing the predicted with the observed mortality rates.
  
  
  RESULTS
  The best accuracy (AUC 0.76) was obtained using a model including only age, left ventricular ejection fraction, serum creatinine, emergency operation and non-isolated coronary operation. The EuroSCORE AUC (0.75) was not significantly different. Calibration and clinical performance were better in the five-factor model than in the EuroSCORE. Only in high-risk patients were 12 factors needed to achieve a good performance.
  
  
  CONCLUSIONS
  Including many factors in multivariable logistic models increases the risk for overfitting, multicollinearity and human error. A five-factor model offers the same level of accuracy but demonstrated better calibration and clinical performance. Models with a limited number of factors may work better than complex models when applied to a limited number of patients.
authors.affiliation: Department of Cardiothoracic-Vascular Anesthesia and Intensive Care, IRCCS Policlinico S. Donato, Milan, Italy. cardioanestesia@virgilio.it
authors.forename: Marco
authors.initials: M
authors.lastname: Ranucci
authors.forename: Serenella
authors.initials: S
authors.lastname: Castelvecchio
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Menicanti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Frigiola
authors.forename: Gabriele
authors.initials: G
authors.lastname: Pelissero
mesh_terms: D000367:Age Factors; D000368:Aged; D015415:Biomarkers / Q000097:blood; D006348:Cardiac Surgical Procedures / Q000401:mortality; D003404:Creatinine / Q000097:blood; D004630:Emergencies; D004812:Epidemiologic Methods; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011300:Preoperative Care / Q000379:methods; D011379:Prognosis; D013318:Stroke Volume
chemical_list: D015415:Biomarkers; D003404:Creatinine