1. Prevention Research Center, Department of Medicine, Stanford University, Stanford, CA, USA (SB)
2. Centers for Health Policy, Primary Care and Outcomes Research, Stanford University, Stanford, CA, USA (SB, JB)
3. Center on Poverty and Inequality, Stanford University, Stanford, CA, USA (SB)
4. Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK (SB)
5. Center for Vulnerable Populations, San Francisco General Hospital, University of California San Francisco, San Francisco, CA, USA (HS)