Time-Location Analysis for Exposure Assessment Studies of Children Using a Novel Global Positioning System Instrument. (Children's Health / Articles)
Elgethun, Kai, Fenske, Richard A., Yost, Michael G., Palcisko, Gary J., Environmental Health Perspectives
Global positioning system (GPS) technology is used widely for business and leisure activities and offers promise for human time-location studies to evaluate potential exposure to environmental contaminants. In this article we describe the development of a novel GPS instrument suitable for tracking the movements of young children. Eleven children in the Seattle area (2-8 years old) wore custom-designed data-logging GPS units integrated into clothing. Location data were transferred into geographic information systems software for map overlay, visualization, and tabular analysis. Data were grouped into five location categories (in vehicle, inside house, inside school, inside business, and outside) to determine time spent and percentage reception in each location. Additional experiments focused on spatial resolution, reception efficiency in typical environments, and sources of signal interference. Significant signal interference occurred only inside concrete/steel-frame buildings and inside a power substation. The GPS instruments provided adequate spatial resolution (typically about 2-3 m outdoors and 4-5 m indoors) to locate subjects within distinct microenvironments and distinguish a variety of human activities. Reception experiments showed that location could be tracked outside, proximal to buildings, and inside some buildings. Specific location information could identify movement in a single room inside a home, on a playground, or along a fence line. The instrument, worn in a vest or in bib overalls, was accepted by children and parents. Durability of the wiring was improved early in the study to correct breakage problems. The use of GPS technology offers a new level of accuracy for direct quantification of time-location activity patterns in exposure assessment studies. Key words: activity pattern, behavior, children, exposure assessment, GIS, GPS, organophosphorous pesticides, time-location, tracking. Environ Health Perspect 111:115-122 (2003). [Online 11 December 2002]
doi: 10.1289/ehp.5350 available via http://dx.doi.org/
Evaluation of children's exposure to environmental health hazards is essential for both epidemiology and risk assessment and has become a recent focus of national concern (1). An essential component of exposure assessment is knowledge of where individuals spend their time. Such time-location information can be linked with pollutant concentration data to produce exposure estimates for well-defined environments, often called microenvironments (2). Conventional time-location analysis has relied on interviews or diaries (3-6). Efforts have been made recently to improve the validity of these methods, including the "shadowing" of subjects with an observer, and use of a beeper to prompt subjects to record time-location data (7,8). Other methods and technologies have been explored but have not proven practical for human exposure studies (9,10). The purpose of the study reported in this article was to identify and test a new method for tracking preschool children throughout the course of a day.
The location of children has most often been documented through parental interviews and diaries (11-13). Although probably adequate for gross location analysis (home/not home), they are not considered reliable for more detailed characterizations (time indoors or outdoors at home or day care, time in vehicle). Evaluation of children's microactivities (e.g., hand-to-mouth behavior) has used videotaping at single locations (14,15), but this approach cannot be applied realistically to track children's locations throughout the day.
Global positioning system technology. The essential aspects of global positioning system (GPS) technology have been described in a report by the U.S. Environmental Protection Agency (16). A summary of how GPS units collect temporal and locational data is provided here. GPS satellites orbit the earth twice every 24 hr transmitting a 50-W signal at 1,575. …