1. Department of Epidemiology and Public Health, Yale University School of Medicine, 60 College Street, P.O. Box 208034, New Haven, Connecticut 06520-8034, Center for Occupational and Environmental Health, 140 Warren Hall, MC-7360, University of CaliforniaBerkeley, Berkeley, California 94720, Division of Nutrition, National Institute of Public Health, Av. Universidad 655, Cuernavaca, Morelos, Mexico 62508, and Institute for Survey Research, Temple University, Philadelphia, Pennsylvania 19122-6099