1. Department of Pediatrics, Stanford University School of Medicine, Suite 100, 770 Welch Rd, Palo Alto, CA 94301, USA
2. School Health Programs Department, San Francisco Unified School District, 1515 Quintara Ave, San Francisco, CA 94116, USA
3. Department of Pediatrics, University of California, Box SFGH, MS 6E/SFGH(nh), San Francisco, CA 94143, USA
4. Cecil G. Sheps Center for Health Services Research, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA