1. K.M. Tomey, PhD, is Assistant Research Scientist, Department of Epidemiology, School of Public Health, University of Michigan, 109 Observatory St, Room 1867, Ann Arbor, MI 48109-2029 (USA).
2. M.R. Sowers, PhD, is John G. Searle Professor of Public Health and Professor of Epidemiology, Department of Epidemiology, School of Public Health, University of Michigan.