1 University of North Carolina School of Medicine, Chapel Hill, NC, USA.
2 Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
3 The North Carolina Translational & Clinical Sciences Institute, Chapel Hill, NC, USA.
4 Carolina Population Center, Chapel Hill, NC, USA.
5 Department of Medicine, Division of Cardiology, UNC Heart and Vascular, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
6 Department of Medicine, Division of Cardiology, UNC Heart and Vascular, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. ross_simpson@med.unc.edu.