1. 1Department of Pediatrics, University of Washington, Seattle, Washington.
2. 2Children's Oncology Group Data and Statistics Center, Department of Biostatistics, University of Florida, Gainesville, Florida.
3. 3Department of Pediatrics, University of Southern California, Los Angeles, California.
4. 4Children's Oncology Group Data and Statistics Center, Monrovia, California.
5. 5Department of Pediatrics, University of Pennsylvania, Philadelphia, Pennsylvania.
6. 6Department of Pediatrics, Duke University, Durham, North Carolina.
7. 7Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada.