Methods
We used the Pediatric Health Information System (PHIS), an electronic
database of children’s hospitals in the US. The study was deemed exempt
by the local Institutional Review Board. De-identified patients under
the age of 21 who underwent HSCT at one of the 42 PHIS hospitals from
2000-2012 were analyzed using data abstracted with ICD-9 codes. All
statistical analyses were performed using SAS software, version 9.3 (SAS
Institute, Cary, NC) or the base R statistical package (R Foundation for
Statistical Computing, Vienna, Austria). All calculated P values
were 2-sided, and P < .05 were considered statistically
significant.