title: Validation and Recalibration of Two Multivariable Prognostic Models for Survival and Independence in Acute Stroke.
abstract: Various prognostic models have been developed for acute stroke, including one based on age and five binary variables ('six simple variables' model; SSVMod) and one based on age plus scores on the National Institutes of Health Stroke Scale (NIHSSMod). The aims of this study were to externally validate and recalibrate these models, and to compare their predictive ability in relation to both survival and independence.
  
  
  
  Data from a large clinical trial of oxygen therapy (n = 8003) were used to determine the discrimination and calibration of the models, using C-statistics, calibration plots, and Hosmer-Lemeshow statistics. Methods of recalibration in the large and logistic recalibration were used to update the models.
  
  
  
  For discrimination, both models functioned better for survival (C-statistics between .802 and .837) than for independence (C-statistics between .725 and .735). Both models showed slight shortcomings with regard to calibration, over-predicting survival and under-predicting independence; the NIHSSMod performed slightly better than the SSVMod. For the most part, there were only minor differences between ischaemic and haemorrhagic strokes. Logistic recalibration successfully updated the models for a clinical trial population.
  
  
  
  Both prognostic models performed well overall in a clinical trial population. The choice between them is probably better based on clinical and practical considerations than on statistical considerations.
authors.affiliation: Institute for Primary Care and Health Sciences, Keele University, Keele, United Kingdom.
authors.forename: Julius
authors.identifier: 0000-0002-1816-1676
authors.initials: J
authors.lastname: Sim
authors.affiliation: Institute for Primary Care and Health Sciences, Keele University, Keele, United Kingdom.
authors.forename: Lucy
authors.initials: L
authors.lastname: Teece
authors.affiliation: Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Martin S
authors.initials: MS
authors.lastname: Dennis
authors.affiliation: Stroke Research in Stoke, University Hospitals of North Midlands NHS Trust, Stoke-on-Trent, United Kingdom.|Institute for Science and Technology in Medicine, Keele University, Keele, United Kingdom.
authors.forename: Christine
authors.initials: C
authors.lastname: Roffe
mesh_terms: D002138:Calibration; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015999:Multivariate Analysis; D010100:Oxygen / Q000627:therapeutic use; D011237:Predictive Value of Tests; D011379:Prognosis; D016016:Proportional Hazards Models; D012372:ROC Curve; D018570:Risk Assessment / Q000379:methods; D012720:Severity of Illness Index; D020521:Stroke / Q000175:diagnosis* / Q000401:mortality*; D016896:Treatment Outcome
chemical_list: D010100:Oxygen