1. From the Department of Medicine, Rush–Presbyterian–St. Luke's Medical Center, Chicago (E.J.L., R.D.R.); the Biostatistics Center, George Washington University, Washington, D.C. (S.-P.L., J.M.L.); and the Department of Medicine, University of Iowa, Iowa City (L.G.H.). Address reprint requests to Dr. Lewis at the Section of Nephrology, 1653 W. Congress Pkwy., Chicago, IL 60615.