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Comparison of global positioning system (GPS) tracking and parent-report diaries to characterize children's time–location patterns


Respondent error, low resolution, and study participant burden are known limitations of diary timelines used in exposure studies such as the National Human Exposure Assessment Survey (NHEXAS). Recent advances in global positioning system (GPS) technology have produced tracking devices sufficiently portable, functional and affordable to utilize in exposure assessment science. In this study, a differentially corrected GPS (dGPS) tracking device was compared to the NHEXAS diary timeline. The study also explored how GPS can be used to evaluate and improve such diary timelines by determining which location categories and which respondents are least likely to record “correct” time–location responses. A total of 31 children ages 3–5 years old wore a dGPS device for all waking hours on a weekend day while their parents completed the NHEXAS diary timeline to document the child's time–location pattern. Parents misclassified child time–location approximately 48% of the time using the NHEXAS timeline in comparison to dGPS. Overall concordance between methods was marginal (κ=0.33–0.35). The dGPS device found that on average, children spent 76% of the 24-h study period in the home. The diary underestimated time the child spent in the home by 17%, while overestimating time spent inside other locations, outside at home, outside in other locations, and time spent in transit. Diary data for time spent outside at home and time in transit had the lowest response concordance with dGPS. The diaries of stay-at-home mothers and mothers working unskilled labor jobs had lower concordance with dGPS than did those of the other participants. The ability of dGPS tracking to collect continuous rather than categorical (ordinal) data was also demonstrated. It is concluded that automated GPS tracking measurements can improve the quality and collection efficiency of time–location data in exposure assessment studies, albeit for small cohorts.

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The authors are grateful to NCG Freeman for providing the complete NHEXAS diary and training materials for administering the diary. Thank you to J. Kissel for review and comments. Special thank you to G. Wist and S.Weppner for field data collection; to the Seattle Early Head Start Centers; and to participating families.

This work was supported by the Agricultural Centers Program of the National Institute for Occupational Safety and Health (Pacific Northwest Agricultural Safety and Health Center, No. 5 U50 OH07544), and by grants from the National Institute of Environmental Health Sciences (P01 ES09601), and the U.S. Environmental Protection Agency (R826886) as part of the University of Washington's Center for Child Environmental Health Risks Research. Although the research described in this article has been funded by a federal agency, it has not been subjected to agency-required peer and policy review and therefore does not necessarily reflect the views of the agencies and no official endorsement should be inferred.

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Correspondence to Kai Elgethun.

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Elgethun, K., Yost, M., Fitzpatrick, C. et al. Comparison of global positioning system (GPS) tracking and parent-report diaries to characterize children's time–location patterns. J Expo Sci Environ Epidemiol 17, 196–206 (2007).

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