[1] Univ N Carolina, Frank Porter Graham Child Dev Ctr, Chapel Hill, NC 27599 USA
[2] Univ N Carolina, Sch Publ Hlth, Chapel Hill, NC 27599 USA
[3] Univ N Carolina, Dept Pediat, Chapel Hill, NC 27599 USA
[4] Univ N Carolina, Dept Allied Hlth Sci, Div Speech & Hearing Sci, Chapel Hill, NC 27599 USA
[5] Univ N Carolina, Dept Psychiat, Chapel Hill, NC 27599 USA
[6] Univ N Carolina, Dept Psychol, Chapel Hill, NC 27599 USA
[7] Univ N Carolina, Sch Nursing, Chapel Hill, NC 27599 USA
[8] Duke Univ, Sch Med, Durham, NC USA