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