1. The University of Texas Medical School, Division of Hematology-Oncology, Houston, TX, USA
2. The Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, MN
3. The University of North Carolina, Collaborative Studies Coordinating Center, Chapel Hill
4. The National Heart, Lung, and Blood Institute, Division of Epidemiology and Clinical Applications, Federal Building, Bethesda, USA