1. Department of Epidemiology & Population Health, Stanford University School of Medicine, Stanford, CA 94305, USA
2. Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD 20892, USA
3. Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health and Department of Health and Human Services, Research Triangle Park, Durham, NC 27709, USA
4. Department of Medicine, University of Colorado Anschutz Medical Campus, Denver, CO 80045, USA