title: External validation of the Intensive Care National Audit & Research Centre (ICNARC) risk prediction model in critical care units in Scotland.
abstract: BACKGROUND
  Risk prediction models are used in critical care for risk stratification, summarising and communicating risk, supporting clinical decision-making and benchmarking performance. However, they require validation before they can be used with confidence, ideally using independently collected data from a different source to that used to develop the model. The aim of this study was to validate the Intensive Care National Audit & Research Centre (ICNARC) model using independently collected data from critical care units in Scotland.
  
  
  METHODS
  Data were extracted from the Scottish Intensive Care Society Audit Group (SICSAG) database for the years 2007 to 2009. Recoding and mapping of variables was performed, as required, to apply the ICNARC model (2009 recalibration) to the SICSAG data using standard computer algorithms. The performance of the ICNARC model was assessed for discrimination, calibration and overall fit and compared with that of the Acute Physiology And Chronic Health Evaluation (APACHE) II model.
  
  
  RESULTS
  There were 29,626 admissions to 24 adult, general critical care units in Scotland between 1 January 2007 and 31 December 2009. After exclusions, 23,269 admissions were included in the analysis. The ICNARC model outperformed APACHE II on measures of discrimination (c index 0.848 versus 0.806), calibration (Hosmer-Lemeshow chi-squared statistic 18.8 versus 214) and overall fit (Brier's score 0.140 versus 0.157; Shapiro's R 0.652 versus 0.621). Model performance was consistent across the three years studied.
  
  
  CONCLUSIONS
  The ICNARC model performed well when validated in an external population to that in which it was developed, using independently collected data.
authors.affiliation: Intensive Care National Audit & Research Centre (ICNARC), Napier House, 24 High Holborn, London, WC1V 6AZ UK.
authors.forename: David A
authors.initials: DA
authors.lastname: Harrison
authors.affiliation: Scottish Intensive Care Society Audit Group, Information Services Division, NHS National Services Scotland, 1 South Gyle Crescent, Edinburgh, EH12 9EB UK ; Directorate of Critical Care, Royal Infirmary of Edinburgh, 51 Little France Crescent, Edinburgh, EH16 5SA UK ; Centre for Population Health Sciences, University of Edinburgh, Medical School, Teviot Place, Edinburgh, EH8 9AG UK.
authors.forename: Nazir I
authors.initials: NI
authors.lastname: Lone
authors.affiliation: Scottish Intensive Care Society Audit Group, Information Services Division, NHS National Services Scotland, 1 South Gyle Crescent, Edinburgh, EH12 9EB UK.
authors.forename: Catriona
authors.initials: C
authors.lastname: Haddow
authors.affiliation: Scottish Intensive Care Society Audit Group, Information Services Division, NHS National Services Scotland, 1 South Gyle Crescent, Edinburgh, EH12 9EB UK.
authors.forename: Moranne
authors.initials: M
authors.lastname: MacGillivray
authors.affiliation: Scottish Intensive Care Society Audit Group, Information Services Division, NHS National Services Scotland, 1 South Gyle Crescent, Edinburgh, EH12 9EB UK.
authors.forename: Angela
authors.initials: A
authors.lastname: Khan
authors.affiliation: Scottish Intensive Care Society Audit Group, Information Services Division, NHS National Services Scotland, 1 South Gyle Crescent, Edinburgh, EH12 9EB UK ; Directorate of Critical Care, Royal Infirmary of Edinburgh, 51 Little France Crescent, Edinburgh, EH16 5SA UK.
authors.forename: Brian
authors.initials: B
authors.lastname: Cook
authors.affiliation: Intensive Care National Audit & Research Centre (ICNARC), Napier House, 24 High Holborn, London, WC1V 6AZ UK.
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Rowan
mesh_terms: D018806:APACHE; D000368:Aged; D000465:Algorithms; D003422:Critical Care / Q000706:statistics & numerical data*; D016208:Databases, Factual; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007362:Intensive Care Units / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012306:Risk; D020379:Risk Adjustment; D018570:Risk Assessment; D012606:Scotland
keywords: Critical care; Intensive care units; Models; Prognosis; Risk adjustment; Severity of illness index; Statistical; Validation studies