The AHS datasets are prepared using SAS software, which allows for different kinds of missing values. In the AHS data, we use this capability to indicate the reason why a value is missing.
Pre-1997:
- 8: Not reported
- 9: Not applicable or Not applicable/Not reported
1997-2013:
SAS files
- B: Not applicable.
- D: Don't know.
- R: Refused.
- N: Not reported (exists for a very few variables, such as HDSB)
ASCII files
- -6: Not applicable
- -9 Not reported
2015 and later:
Starting in 2015, B, D, R, ‘.’, or ‘’, and blank were replaced with M and N in the SAS files:
- M = what was formerly a D, R, ‘.’, or ‘’(not reported rows in published tables)
- N = what was formerly a B or blank (not applicable)
ASCII files:
- -9 or Blank = Not reported
- -6 = Not applicable