1. Hubert Department of Global Health, Rollins School of Public Health, Emory University, Atlanta, GA 30322
2. Institute of Nutrition of Central America and Panama, Guatemala City Zona 11, Guatemala
3. Department of Economics, Middlebury College, Middlebury, VT 05753
4. Instituto Nacional de Salud Pública, Cuernavaca, Morelos CP 62508, Mexico