1 Department of Medicine, Veterans Affairs Palo Alto Health Care System, Palo Alto, California.
2 Department of Medicine, Stanford University, Palo Alto, California.
3 University of North Carolina Kidney Center, Division of Nephrology and Hypertension, Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina.
4 Cecil G. Sheps Center for Health Services Research, University of North Carolina, Chapel Hill, North Carolina.