Admission day of the week (ADAYWK) is calculated from the admission date (ADATE). If ADAYWK cannot be calculated (ADATE is missing or invalid), then:

• ADAYWK is set to the supplied admission day of the week, if available.
• ADAYWK is missing (.) if the supplied admission day of week is missing.
• If ADAYWK is out of range (ADAYWK NE 1-7) or nonnumeric, it is set to invalid (.A).
• In the 1988-1997 HCUP files, if the data source does not provide the admission date or admission day of week, then ADAYWK is set to unavailable from source (.B).

Beginning in the 1998 HCUP files, the data element ADAYWK is replaced by admission weekend (AWEEKEND).