title: Cautions in the use of antecedents as surrogates for confounders.
abstract: When lacking information on confounding variables, epidemiologists have used surrogates which are antecedents of both the exposures and confounders of interest. The usefulness of this strategy is explored in a series of scenarios for a prospective epidemiologic study wherein risk ratios relating antecedent to confounder, antecedent to exposure, and confounder to exposure were varied. Antecedent-adjusted, confounder-adjusted, and crude risk ratios were calculated and compared. The antecedent-adjusted risk ratio was useful, that is, was closer to the confounder-adjusted risk ratio than was the crude risk ratio, in 1,067 (49%) of 2,187 scenarios. The antecedent-adjusted risk ratio, the crude risk ratio, and the risk ratio relating confounder to exposure together predicted the usefulness of the antecedent (or any variable) as a confounder proxy. The antecedent was useful in 97% of scenarios wherein: 1) the antecedent-adjusted risk ratio was less than the crude risk ratio, and the risk ratio relating confounder to exposure was greater than 1.0, or 2) the antecedent-adjusted risk ratio was greater than the crude risk ratio, and the risk ratio relating confounder to exposure was less than 1.0. In the remaining scenarios, it was useful only 5% of the time.
authors.affiliation: Department of Epidemiology, University of Washington, Seattle 98195.
authors.forename: B W
authors.initials: BW
authors.lastname: Alderman
authors.forename: A E
authors.initials: AE
authors.lastname: Barón
authors.forename: D A
authors.initials: DA
authors.lastname: Savitz
mesh_terms: D015984:Causality; D015986:Confounding Factors, Epidemiologic; D004812:Epidemiologic Methods; D006801:Humans; D011446:Prospective Studies; D012307:Risk Factors