1 Human Biology Program, Stanford University, Stanford, CA, USA.
2 Stanford Aging and Ethnogeriatrics (SAGE), Research Center, School of Medicine, Stanford University, Stanford, CA 94305, USA; Stanford Center for Population Health Sciences, School of Medicine, Stanford University, Stanford, CA 94305, USA.
3 School of Public Health, University of Nevada, Reno, NV, USA.
4 Department of Global Health and Development, London School of Hygiene and Tropical Medicine, London, UK.
5 Population Council Zambia, Lusaka, Zambia.
6 Global Center for Gender Equality, School of Medicine, Stanford University, Stanford, CA 94305, USA; Department of Pediatrics, School of Medicine, Stanford University, Stanford, CA 94305, USA. Electronic address: gdarmsta@stanford.edu.