Abstract
The National Human Exposure Assessment Survey (NHEXAS) field study in EPA Region V (one of three NHEXAS field studies) provides extensive exposure data on a representative sample of 249 residents of the Great Lakes states. Concentration data were obtained for both metals and volatile organic compounds (VOCs) from multiple environmental media and from human biomarkers. A variance model for the logarithms of concentration measurements is used to define intraclass correlations between observations within primary sampling units (PSUs) (nominally counties) and within secondary sampling units (SSUs) (nominally Census blocks). A model for the total cost of the study is developed in terms of fixed costs and variable costs per PSU, SSU, and participant. Intraclass correlations are estimated for media and analytes with sufficient sample sizes. We demonstrate how the intraclass correlations and variable cost components can be used to determine the sample allocation that minimizes cost while achieving pre-specified precision constraints for future studies that monitor environmental concentrations and human exposures for metals and VOCs.
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Notes
For the urine measurements, the day 3 and day 7 data were combined, and an additional component of variance, between days within persons, was estimated but not reported.
Measurable values were defined as observations exceeding the detection limit defined by the laboratory reporting the data. Specific definitions varied by type of measurement and chemical class.
No values were replaced for 63.5% of the outcomes. For those outcomes that did need replacement, at most 11.3 percent of the values were replaced.
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Acknowledgements
The United States Environmental Protection Agency through its Office of Research and Development funded and collaborated in the research described here under Contract Number 68-D-99-008 and Assistance Agreement Number CR821902 to Research Triangle Institute. It has been subjected to Agency review and approved for publication. We thank C.A. Clayton for preparation of the statistical analysis database, B. Buckley for estimation of costs for analysis of the dust samples, and C. Suerken for estimation of the variance components. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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Whitmore, R., Pellizzari, E., Zelon, H. et al. Cost/variance optimization for human exposure assessment studies. J Expo Sci Environ Epidemiol 15, 464–472 (2005). https://doi.org/10.1038/sj.jea.7500424
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DOI: https://doi.org/10.1038/sj.jea.7500424
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