Use of GIS in Sampling Stratification Selection for the National Children’s Study Waukesha Vanguard Center
National Institute of Child Health and Human Development
The National Children’s Study (NCS) will study the complex relationship between health and the environment for approximately 100,000 children and their families. Enrollment will begin before birth and follow-up will continue for at least 21 years. After much scientific discussion and consultation regarding the scope and design of the NCS, a stratified national probability sampling design was considered to obtain:
- an adequate range of exposures
- socioeconomic, racial/ethnic/geographic diversity
- population subgroups of interest
Each study center had discretion on determining its sampling frame for constructing equal-size (equal number of births) segments and strata.
At the NCS Waukesha County Vanguard Center (NCS-WVC), we employed geographic information systems (GIS) to identify strata that were potentially relevant to children’s health. Specifically, eight primary strata corresponding to geographic divisions of the county that demonstrate inter-stratum variability and intra-stratum homogeneity based on maps of geographic, environmental and demographic characteristics were identified. Strata with larger populations (4 of the 8 primary strata) were further stratified using US census block group characteristics with:
- importance as potential risk factors affecting fetal or child health and development
- geographic variability within the respective initial stratum
- contiguity of the defined quantiles for these variables within the stratum
The boundaries of segments were further adjusted by incorporating estimated births from new housing developments in the years between the last available birth data and study recruitment.
The application of GIS to sampling in environmental epidemiology allows visual representation and active participation of a wide range of investigators and community members in sample stratification decision-making
For more information, contact:
Jane McElroy, PhD
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