1. Arsenic Health Effects Research Program, School of Public Health, University of California, Berkeley, Berkeley, California, USA
2. Departamento de Salud Pública, Escuela de Medicina, and
3. Departamento de Estadística, Facultad de Matemáticas, Universidad Católica de Chile, Santiago, Chile
4. Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, California, USA