1. Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, Michigan, USA
2. Division of Statistics, Center for Evaluation Research and Surveys, National Institute of Public Health, Cuernavaca, Mexico
3. Centers for Disease and Control and Prevention, Atlanta, Georgia, USA
4. Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA
5. Ministry of Health, Mexico City, Mexico