1. Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
2. St. Christopher’s Hospital for Children, Philadelphia, Pennsylvania, USA
3. Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
4. Departments of Medicine and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
5. Department of Emergency Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
6. Departments of Medical Education and Sociology, University of Illinois-Chicago, Chicago, USA