1. International Food Policy Research Institute, 2033 K Street, NW, Washington, DC 20006 (e-mail: )
2. UNICEF Office of Research—Innocenti, Piazza S.S. Annunizata 12, 50121 Florence, Italy (e-mail: )
3. London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK (e-mail: )