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A NEW METHOD OF LONGITUDINAL DIARY ASSEMBLY FOR HUMAN EXPOSURE MODELING
Citation:
GLEN, G., L. SMITH, K. K. ISAACS, T. R. MCCURDY, AND J. LANGSTAFF. A NEW METHOD OF LONGITUDINAL DIARY ASSEMBLY FOR HUMAN EXPOSURE MODELING. Journal of Exposure Science and Environmental Epidemiology . Nature Publishing Group, London, Uk, 18(3):299-311, (2008).
Impact/Purpose:
The overall goal of this work is to develop information to assess potential environmental health risks and susceptibility in the aging population. Initial work will be directed toward developing information that can be used to identify and characterize what is known about activity, exposure, and dose for key life stages in the aging population and to identify key data gaps to be addressed through further research. Specific research objectives have been identified to address four discrete elements of the environmental paradigm for an aging population.
1) Identify key chemical and biological stressors in the older adult population, compile extant information on exposures to these agents and the extent to which they may be different in aging and other populations, and identify key gaps in our knowledge of exposure to important stressors.
2) Identify the key life stages in the older adult population with regard to exposures and susceptibilities to chemical and biological stressors. Compile activity pattern and physiological information for older Americans in key life stages, including information on physical activity, dietary intakes, pharmaceutical use, and other possible stressors that may impact exposures and/or susceptibility. Identify key gaps in our knowledge of activities in subpopulations of the aging by life stages.
3) Incorporate changes in physiological parameters that result from aging in physiologically-based pharmacokinetic models. Assess the relative sensitivity of aging-related changes in parameters for generation of dose estimates. Determine which parameters may require additional knowledge to improve the models.
4) Provide information developed for exposure, activity, and pharmacokinetics to extend existing exposure and PBPK models to aging populations and susceptible subpopulations at different life stages for use in risk assessment. Also, appropriate information will be provided for incorporation into an Older Adults Exposure Factors Handbook being prepared by NCEA.
Description:
Human exposure time-series modeling requires longitudinal time-activity diaries to evaluate the sequence of concentrations encountered, and hence, pollutant exposure for the simulated individuals. However, most of the available data on human activities are from cross-sectional surveys that typically sample one day per person. A procedure is needed for combining cross-sectional activity data into multiple-day (longitudinal)sequences that can capture day-to-day variability in human exposures. Properly accounting for intra- and inter-individual variability in these sequences can have a significant effect on exposure estimates and on the resulting health risk assessments. This paper describes a new method of developing such longitudinal sequences, based on ranking one-day activity diaries with respect to a user-chosen key variable. Two statistics, "D" and "A", are targeted. The D statistic reflects the relative importance of within- and between-person variance with respect to the key variable. The A statistic quantifies the day-to-day (lag-one) autocorrelation. The user selects appropriate target values for both D and A. The new method then stochastically assembles longitudinal diaries that collectively meet these targets. Based upon numerous simulations, the D and A targets are closely attained for exposure analysis periods >30 days in duration, and reasonably well for shorter simulation periods. Longitudinal diary data from a field study suggest that D and A are stable over time, and perhaps over cohorts as well. The new method can be used with any cohort definitions and diary pool assignments, making it easily adaptable to most exposure models. Implementation of the new method in its basic form is described, and various extensions beyond the basic form are discussed.