1. Epidemiology Branch, National Institute of Environmental Health Sciences (NIEHS), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Research Triangle Park, North Carolina, USA
2. Social & Scientific Systems, Inc., Durham, North Carolina, USA
3. Westat, Durham, North Carolina, USA
4. Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway
5. Biostatistics and Computational Biology Branch, NIEHS, NIH, DHHS, Research Triangle Park, North Carolina, USA