1. ^aDepartment of Geography and School of Rural Public Health, Texas A&M University, College Station, TX, USA
2. ^bDepartment of Environmental and Occupational Health Sciences, School of Public Health and Community Medicine, University of Washington, Seattle, WA, USA
3. ^cDepartment of Geography, University of Washington, Seattle, WA, USA

Correspondence: Dr. Kai Elgethun, Department of Geography and School of Rural Public Health, Texas A&M University, College Station, MS 3147, TX 77843-3147, USA. Tel.: +1979 458 3030; Fax: +1979 862 4487; E-mail: elgethun@geog.tamu.edu

Received 24 April 2005; Accepted 11 April 2006; Published online 14 June 2006.

Abstract

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 (=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.