title: A straightforward approach to designing a scoring system for predicting length-of-stay of cardiac surgery patients.
abstract: BACKGROUND
  Length-of-stay prediction for cardiac surgery patients is a key point for medical management issues, such as optimization of resources in intensive care units and operating room scheduling. Scoring systems are a very attractive family of predictive models, but their retraining and updating are generally critical. The present approach to designing a scoring system for predicting length of stay in intensive care aims to overcome these difficulties, so that a model designed in a given scenario can easily be adjusted over time or for internal purposes.
  
  
  METHODS
  A naïve Bayes approach was used to develop a simple scoring system. A set of 36 preoperative, intraoperative and postoperative variables collected in a sample of 3256 consecutive adult patients undergoing heart surgery were considered as likely risk predictors. The number of variables was reduced by selecting an optimal subset of features. Scoring system performance was assessed by cross-validation.
  
  
  RESULTS
  After the selection process, seven variables were entered in the prediction model, which showed excellent discrimination, good generalization power and suitable sensitivity and specificity. No significant difference was found between AUC of the training and testing sets. The 95% confidence interval for AUC estimated by the BCa bootstrap method was [0.841, 0.883] and [0.837, 0.880] in the training and testing sets, respectively. Chronic dialysis, low postoperative cardiac output and acute myocardial infarction proved to be the major risk factors.
  
  
  CONCLUSIONS
  The proposed approach produced a simple and trustworthy scoring system, which is easy to update regularly and to customize for other centers. This is a crucial point when scoring systems are used as predictive models in clinical practice.
authors.affiliation: Department of Medical Biotechnologies, University of Siena, Viale Bracci 53100, Siena, Italy. paolo.barbini@unisi.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Barbini
authors.forename: Emanuela
authors.initials: E
authors.lastname: Barbini
authors.forename: Simone
authors.initials: S
authors.lastname: Furini
authors.forename: Gabriele
authors.initials: G
authors.lastname: Cevenini
mesh_terms: D006348:Cardiac Surgical Procedures / Q000706:statistics & numerical data*; D003661:Decision Support Techniques; D006801:Humans; D007362:Intensive Care Units / Q000706:statistics & numerical data*; D007902:Length of Stay / Q000706:statistics & numerical data*; D015233:Models, Statistical