1. Department of Statistics, Texas A&M University, College Station, Texas 77843‐3143, U.S.A.
2. Department of Statistics, University of Missouri, Columbia, Missouri 65211‐6100, U.S.A.
3. Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 6120 Executive Boulevard, EPS 8038 Rockville, Maryland 20852, U.S.A.