1. School of Public Health, University of California at Berkeley, Berkeley, CA 94720, USA.
2. Harvard University School of Public Health, Boston, MA 02115, USA.
3. ETR Associates, Scotts Valley, CA 95066, USA.
4. Department of Sociology, University of California at Berkeley, Berkeley, CA 94720, USA.
5. Philip R. Lee Institute for Health Policy Studies, University of California at San Francisco, San Francisco, CA 94143, USA.
6. San Francisco Department of Public Health, San Francisco, CA 94103, USA.
7. Department of Family and Community Medicine, University of California at San Francisco, San Francisco, CA 94143, USA.