Data files were prepared and validated according to protocol specified by the AHRQ for the HCUP SID files ( HCUP Databases, 2009 ). Data were then filtered by inclusion and exclusion criteria. The resulting data set was examined for distribution of variables of interest and missing data. Each patient record allowed for the inclusion of 25 diagnoses, all of which were examined for injuries and complications. A maximum of 29 AHRQ-designated comorbid (preexisting) conditions, unrelated to the primary diagnosis or reason for admission, are included for each patient record. These are a separate designation from diagnoses and complications.