1. Stanford Prevention Research Center, Department of Medicine and Department of Health Research and Policy, Stanford University School of Medicine and Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, CA 94305, USA.
2. Office of Public Health Genomics, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA; and Division of Cancer Control and Population Sciences, National Cancer Institute, National Institutes of Health, Bethesda, MD 20852, USA.