title: A potential pitfall in control of covariates in epidemiologic studies.
abstract: Control of covariates is essential in nonexperimental epidemiologic studies. Important covariates, such as smoking or alcohol consumption, often are crudely categorized in epidemiologic analyses. In this paper, I illustrate by both hypothetical and empirical examples that control of crudely categorized covariates can yield strongly misleading results. In particular, I show that, under certain conditions, control for crudely classified covariates can even be worse than not controlling for such covariates at all. I conclude that covariate specification is an issue that requires much more care than it commonly receives in epidemiologic analyses.
authors.affiliation: Department of Epidemiology, University of Ulm, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Brenner
mesh_terms: D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D015987:Effect Modifier, Epidemiologic; D004812:Epidemiologic Methods; D006801:Humans