1 From the Department of Epidemiology and Biostatistics (D.G.), School of Public Health, Imperial College London, United Kingdom; Department of Medicine (M.V.), University of Pennsylvania Perelman School of Medicine, Philadelphia; and Corporal Michael J. Crescenz VA Medical Center (M.V.), Philadelphia, PA. dipender.gill@imperial.ac.uk.
2 From the Department of Epidemiology and Biostatistics (D.G.), School of Public Health, Imperial College London, United Kingdom; Department of Medicine (M.V.), University of Pennsylvania Perelman School of Medicine, Philadelphia; and Corporal Michael J. Crescenz VA Medical Center (M.V.), Philadelphia, PA.