title: What do we mean by validating a prognostic model?
abstract: Prognostic models are used in medicine for investigating patient outcome in relation to patient and disease characteristics. Such models do not always work well in practice, so it is widely recommended that they need to be validated. The idea of validating a prognostic model is generally taken to mean establishing that it works satisfactorily for patients other than those from whose data it was derived. In this paper we examine what is meant by validation and review why it is necessary. We consider how to validate a model and suggest that it is desirable to consider two rather different aspects - statistical and clinical validity - and examine some general approaches to validation. We illustrate the issues using several case studies.
authors.affiliation: ICRF Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Old Road, Headington, Oxford OX3 7LF, UK. altman@icrf.icnet.uk
authors.forename: D G
authors.initials: DG
authors.lastname: Altman
authors.forename: P
authors.initials: P
authors.lastname: Royston
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control; D000368:Aged; D001249:Asthma / Q000473:pathology; D006259:Craniocerebral Trauma / Q000401:mortality; D003661:Decision Support Techniques; D006801:Humans; D009203:Myocardial Infarction / Q000401:mortality; D011379:Prognosis; D011446:Prospective Studies; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012307:Risk Factors