1. AI Greenspan, PT, MPH, DrPH, is Senior Scientist, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, 4770 Buford Hwy NE, Mailstop K-63, Atlanta, GA 30341 (USA)
2. SL Wolf, PT, PhD, FAPTA, is Professor, Department of Rehabilitation Medicine, Emory University School of Medicine, Atlanta, Ga
3. ME Kelley, PhD, is Research Assistant Professor, Department of Biostatistics, Rollins School of Public Health, Emory University, Atlanta, Ga
4. M O'Grady, MD, is currently in private practice. Dr O'Grady was Assistant Professor, Department of Rehabilitation Medicine, Emory University School of Medicine, at the time of the study