This mapping of comorbidities to ICD-9 codes is dervied directly
from SAS code provided by AHRQ, and translated into this R data structure.
Beyond ahrqComorbid, this includes all the HTN, CHF and renal subgroups,
not rolled into their parent categories. This resolution is not needed in
typical usage: ahrqComorbid is probably what you want.
list of character vectors, each named by co-morbidity