[1] St Jude Childrens Res Hosp, Dept Behav Med, Memphis, TN 38105 USA
[2] Hosp Sick Children, Dept Psychol, Toronto, ON M5G 1X8, Canada
[3] Nationwide Childrens Hosp, Ctr Biobehav Hlth, Res Inst, Columbus, OH USA
[4] St Jude Childrens Res Hosp, Dept Biostat, Memphis, TN 38105 USA
[5] Hosp Sick Children, Dept Pediat, Toronto, ON M5G 1X8, Canada
[6] Univ Penn, Childrens Hosp Philadelphia, Sch Med, Div Oncol, Philadelphia, PA 19104 USA