1. Center for Public Health and Environmental Assessment, Office of Research and Development, US Environmental Protection Agency (US EPA), Research Triangle Park, North Carolina, USA
2. Department of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA
3. Industrial Economics, Inc., Cambridge, Massachusetts, USA
4. Office of Air Quality Planning and Standards, Office of Air and Radiation, US EPA, Research Triangle Park, North Carolina, USA