1. Poverty, Health, and Nutrition Division, International Food Policy Research Institute, Washington, DC, 20006
2. Center for Evaluation Research and Surveys, Col. Sta. María Ahuacatitlán, CP 62100, Cuernavaca, Morelos, México
3. Center for Nutrition and Health Research, National Institute of Public Health, Col. Sta. María Ahuacatitlán, CP 62100, Cuernavaca, Morelos, México