1. The University of North Carolina at Chapel Hill, Injury Prevention Research Center, Chapel Hill, North Carolina;
2. The University of North Carolina at Chapel Hill, Department of Family Medicine, Chapel Hill, North Carolina;
3. Developmental Neurosciences and Child Health, Child and Family Research Institute, British Columbia Children’s Hospital, University of British Columbia Faculty of Medicine, Vancouver, British Columbia, Canada; and
4. Department of Pediatrics, University of Colorado and the Kempe Center, Aurora, Colorado