Misspecification of within-area exposure distribution in ecological Poisson models |
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Authors: | Léa Fortunato Chantal Guihenneuc-Jouyaux Margot Tirmarche Dominique Laurier Denis Hémon |
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Institution: | (1) INSERM, U754, 16 av Paul Vaillant-Couturier, 94807 Villejuif cedex, France;(2) Université Paris Sud, IFR69, 16 av Paul Vaillant-Couturier, 94807 Villejuif cedex, France;(3) CNRS UMR 8145, UFR Biomédicale, Université Paris 5, 45 rue des Saint-Pères, 75006 Paris, France;(4) IRSN/DRPH/SRBE/LEPID, BP17, 92262 Fontenay-aux-Roses, France |
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Abstract: | Ecological studies enable investigation of geographic variations in exposure to environmental variables, across groups, in
relation to health outcomes measured on a geographic scale. Such studies are subject to ecological biases, including pure
specification bias which arises when a nonlinear individual exposure-risk model is assumed to apply at the area level. Introduction
of the within-area variance of exposure should induce a marked reduction in this source of ecological bias. Assuming several
measurements per area of exposure and no confounding risk factors, we study the model including the within-area exposure variability
when Gaussian within-area exposure distribution is assumed. The robustness is assessed when the within-area exposure distribution
is misspecified. Two underlying exposure distributions are studied: the Gamma distribution and an unimodal mixture of two
Gaussian distributions. In case of strong ecological association, this model can reduce the bias and improve the precision
of the individual parameter estimates when the within-area exposure means and variances are correlated. These different models
are applied to analyze the ecological association between radon concentration and childhood acute leukemia in France.
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Keywords: | Ecological association Ecological bias Robustness Within-area exposure variability |
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