1. Center for Social Epidemiology and Population Health, Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor
2. Department of Internal Medicine, School of Medicine, University of Michigan, Ann Arbor
3. Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor
4. Veterans Affairs Ann Arbor Center for Clinical Management Research, Ann Arbor, Michigan
5. Survey Research Center, Institute for Social Research, University of Michigan, Ann Arbor
6. MRC (Medical Research Council)/Wits Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa