[1] Univ Memphis, Sch Publ Hlth, Div Epidemiol Biostat & Environm Hlth, 222 Robison Hall, Memphis, TN 38111 USA
[2] Univ N Carolina, Gillings Sch Global Publ Hlth, Dept Epidemiol, Chapel Hill, NC 27515 USA
[3] Washington Univ, Sch Med, Dept Surg, St Louis, MO 63110 USA
[4] Ann & Robert H Lurie Childrens Hosp Chicago, Div Hematol Oncol Neurooncol & Stem Cell Transpla, Chicago, IL 60611 USA
[5] Vanderbilt Univ, Dept Pediat, Nashville, TN USA
[6] Vanderbilt Univ, Dept Hlth Policy, 221 Kirkland Hall, Nashville, TN 37235 USA
[7] St Jude Childrens Res Hosp, Dept Hematol, 332 N Lauderdale St, Memphis, TN 38105 USA