1. Department of Pediatrics, Boston Medical Center, Boston, Massachusetts;
2. Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas;
3. Department of Pediatrics, School of Medicine, University of Maryland, Baltimore, Maryland;
4. Department of Health Management and Policy, School of Public Health, Drexel University, Philadelphia, Pennsylvania;
5. Department of Pediatrics, Hennepin County Medical Center, Minneapolis, Minnesota; and
6. Data Coordinating Center, School of Public Health, Boston University, Boston, Massachusetts