[1] Univ Calif San Francisco, Dept Epidemiol & Biostat, 550 16th St,Second Floor, San Francisco, CA 94158 USA
[2] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA USA
[3] Boston Univ, Sch Publ Hlth, Dept Epidemiol, Boston, MA USA
[4] Oregon State Univ, Sch Biol & Populat Hlth Sci, Coll Publ Hlth & Human Sci, Corvallis, OR 98331 USA
[5] UCL, Dept Epidemiol & Publ Hlth, London, England
[6] Stanford Univ, Dept Epidemiol & Populat Hlth, Sch Med, Stanford, CA USA
[7] JAMA, Chicago, IL 60611 USA