[1] Univ Calif San Francisco, Sch Med, Inst Hlth Policy Studies, San Francisco, CA 94109 USA
[2] Univ Calif San Francisco, Sch Med, Dept Pediat, San Francisco, CA 94109 USA
[3] Univ Calif Los Angeles, Sch Med, Dept Pediat, Los Angeles, CA 90024 USA
[4] Univ Calif Los Angeles, Sch Publ Hlth, Los Angeles, CA 90024 USA