[1] Univ Washington, Div Med Genet, Seattle, WA 98195 USA
[2] Univ Washington, Dept Biostat, Seattle, WA 98195 USA
[3] Univ Texas, MD Anderson Canc Ctr, Dept Epidemiol, Houston, TX USA
[4] Univ Texas, MD Anderson Canc Ctr, Dept Biomath, Houston, TX USA