title: Analysis by categorizing or dichotomizing continuous variables is inadvisable: an example from the natural history of unruptured aneurysms.
abstract: In medical research analyses, continuous variables are often converted into categoric variables by grouping values into ≥2 categories. The simplicity achieved by creating ≥2 artificial groups has a cost: Grouping may create rather than avoid problems. In particular, dichotomization leads to a considerable loss of power and incomplete correction for confounding factors. The use of data-derived "optimal" cut-points can lead to serious bias and should at least be tested on independent observations to assess their validity. Both problems are illustrated by the way the results of a registry on unruptured intracranial aneurysms are commonly used. Extreme caution should restrict the application of such results to clinical decision-making. Categorization of continuous data, especially dichotomization, is unnecessary for statistical analysis. Continuous explanatory variables should be left alone in statistical models.
authors.affiliation: Department of Radiology, Interventional Neuroradiology Research Unit, International Consortium of Neuroendovascular Centres, University of Montreal, CHUM Notre-Dame Hospital, Quebec, Canada.
authors.forename: O
authors.initials: O
authors.lastname: Naggara
authors.forename: J
authors.initials: J
authors.lastname: Raymond
authors.forename: F
authors.initials: F
authors.lastname: Guilbert
authors.forename: D
authors.initials: D
authors.lastname: Roy
authors.forename: A
authors.initials: A
authors.lastname: Weill
authors.forename: D G
authors.initials: DG
authors.lastname: Altman
mesh_terms: D017542:Aneurysm, Ruptured / Q000175:diagnosis* / Q000453:epidemiology*; D015982:Bias; D003627:Data Interpretation, Statistical; D006801:Humans; D002532:Intracranial Aneurysm / Q000175:diagnosis* / Q000453:epidemiology*; D015995:Prevalence; D016016:Proportional Hazards Models; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D012680:Sensitivity and Specificity