Affiliation: | 1. Department of Mathematics and Statistics, Mount Holyoke College, South Hadley, MA, U.S.A.;2. Department of Computer Science, University of Massachusetts, Amherst, MA, U.S.A.;3. Department of Biostatistics and Epidemiology, University of Massachusetts, Amherst, MA, U.S.A.;4. Department of Medicine, University of Pennsylvania, Philadelphia, PA, U.S.A. |