[1] Univ N Carolina, Dept Family Med, Chapel Hill, NC 27515 USA
[2] UNC Gillings Sch Global Publ Hlth, Dept Epidemiol, Chapel Hill, NC USA
[3] UNC Gillings Sch Global Publ Hlth, Dept Hlth Behav, Chapel Hill, NC USA
[4] RTI Int, Res Triangle Pk, NC USA