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Open Access Methodology

Estimating equations for biomarker based exposure estimation under non-steady-state conditions

Scott M Bartell12* and Wesley O Johnson2

Author Affiliations

1 Program in Public Health, University of California, Irvine, CA 92697-3957, USA

2 Department of Statistics, University of California, Irvine, CA 92697-1250, USA

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Environmental Health 2011, 10:57  doi:10.1186/1476-069X-10-57

Published: 13 June 2011

Abstract

Unrealistic steady-state assumptions are often used to estimate toxicant exposure rates from biomarkers. A biomarker may instead be modeled as a weighted sum of historical time-varying exposures. Estimating equations are derived for a zero-inflated gamma distribution for daily exposures with a known exposure frequency. Simulation studies suggest that the estimating equations can provide accurate estimates of exposure magnitude at any reasonable sample size, and reasonable estimates of the exposure variance at larger sample sizes.