1. Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
2. School of Public Health, University of Minnesota, Minneapolis, Minnesota, USA
3. Bayer CropScience, Research Triangle Park, North Carolina, USA
4. Battelle Memorial Institute, Columbus, Ohio, USA
5. Emory University, Atlanta, Georgia, USA