Usage: For a sample characteristic in which information for a particular factor is not available, or not applicable. Intended to be a safer version than "NA", "null" or "None" which may cause unexpected side-effects in programming languages if not properly escaped.
Usage: For a sample characteristic in which information for a particular factor is not available, or not applicable. Intended to be a safer version than "NA", "null" or "None" which may cause unexpected side-effects in programming languages if not properly escaped.