1. Division of Biometrics VI; Center for Drug Evaluation and Research, Food and Drug Administration; Rockville MD 20852 U.S.A.
2. The Biostatsitics Center; The George Washington University; 6110 Executive Blvd., Suite 750 Rockville MD 20852 U.S.A.
3. Department of Statistics
4. Department of Biostatistics and Epidemiology; The George Washington University