[1] Life Expectancy Project, San Francisco, CA USA
[2] Univ Calif Berkeley, Dept Biostat, Berkeley, CA 94720 USA
[3] Univ Calif San Francisco, Dept Pediat, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Dept Neurol, San Francisco, CA 94143 USA
[5] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA