Michael R. Kramer and Carol R. Hogue are with the Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA. Lance A. Waller is with the Department of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University. Anne L. Dunlop is with the Department of Family and Preventive Medicine, School of Medicine, Emory University.