Affiliation: | 1. Department of Epidemiology and Biostatistics, School of Public Health, Indiana University, Bloomington, Indiana, USA;2. Institute of Industrial Science, The University of Tokyo, Tokyo, JapanMuch of the work on this paper was done while Keisuke Ejima and David B. Allison were employed at their previous institution, The University of Alabama at Birmingham.;3. Department of Mathematical Sciences, United States Military Academy, West Point, New York, USA |