1. Department of Epidemiology, University of Washington, Seattle, WA 98185, USA
2. Seattle Epidemiologic Research & Information Center, VA Puget Sound, Seattle, WA 98108, USA
3. Department of Biostatistics, University of Washington, Seattle, WA 98195, USA
4. Department of Mathematics & Statistics, Georgetown University, Washington, DC 20057, USA
5. Department of Occupational & Environmental Health Sciences, University of Washington, Seattle, WA 98195, USA
6. Center for Perinatal Studies, Swedish Medical Center, Seattle, WA 98104, USA
7. Department of Epidemiology, Harvard TH Chan School of Public Health, Boston, MA 02115, USA