[1] Emory Univ, Emory Childrens Ctr, Sch Med, Dept Pediat, 2015 Uppergate Dr NE, Atlanta, GA 30322 USA
[2] Childrens Healthcare Atlanta, AFLAC Canc & Blood Disorders Ctr, Atlanta, GA USA
[3] Univ N Carolina, Dept Biostat, Chapel Hill, NC USA
[4] Univ N Carolina, Cecil G Sheps Ctr Hlth Serv Res, Chapel Hill, NC USA
[5] Univ Calif, Sch Social Sci Humanities & Arts, Merced, CA USA
[6] Univ N Carolina, Sch Med, Div Gen Med & Clin Epidemiol, Chapel Hill, NC USA
[7] Univ N Carolina, Dept Hlth Policy & Management, Chapel Hill, NC USA