1. National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD, USA;
2. United States Public Health Service, Rockville, MD, USA;
3. Division of Intramural Research, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA;
4. Department of Pediatrics, UCONN Health Farmington, CT and Connecticut Children's Medical Center, Hartford, CT, USA;
5. Social & Scientific Systems, Durham, NC, USA;
6. Department of Family Medicine and Population Health, the Virginia Commonwealth University, Richmond, VA, USA;
7. National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV, USA