1 Harvard Injury Control Research Center, Department of Health Policy and Management, Harvard T. H. Chan School of Public Health, Boston, Mass. Electronic address: cbarber@hsph.harvard.edu.
2 Harvard Injury Control Research Center, Department of Health Policy and Management, Harvard T. H. Chan School of Public Health, Boston, Mass.
3 Harvard Injury Control Research Center, Department of Health Policy and Management, Harvard T. H. Chan School of Public Health, Boston, Mass; Department of Health Sciences, Northeastern University, Boston, Mass.