[1] Univ S Carolina, Sch Med, Dept Family & Prevent Med, Columbia, SC 29208 USA
[2] Univ N Carolina, Dept Med, Chapel Hill, NC 27515 USA
[3] Univ N Carolina, Dept Biostat, Chapel Hill, NC 27515 USA
[4] Univ S Carolina, Arnold Sch Publ Hlth, S Carolina Rural Hlth Res Ctr, Columbia, SC 29208 USA
[5] Univ S Carolina, Arnold Sch Publ Hlth, Dept Hlth Serv Policy & Management, Columbia, SC 29208 USA