1. Department of Biostatistics St. Jude Children's Research Hospital Memphis Tennessee USA
2. Public Health Research Group University of Alicante Alicante Spain
3. Clinical Research Division Fred Hutchinson Cancer Research Center Seattle Washington USA
4. Department of Pediatrics Division of Hematology/Oncology, University of Washington School of Medicine Seattle Washington USA
5. Department of Epidemiology and Cancer Control St. Jude Children's Research Hospital Seattle Washington USA
6. Department of Oncology St. Jude Children's Research Hospital Memphis Tennessee USA