Affiliation: | (1) Division of Biostatistics and Epidemiology, Department of Health Evaluation Sciences, University of Virginia School of Medicine, Hospital West Complex, Room. 3181, P.O. Box 800717, Charlottesville, VA 22908-0717, USA;(2) Insightful Corporation, 2505 Meridian Parkway Suite 175, Durham, NC 27713, USA |