Department of Mathematics and Statistics, Williams College, Williamstown, MA, USA.|Department of Health Sciences Research, Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN, USA.|Department of Genomic Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.|Department of Biostatistics and Biomathematics Program, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA.