Which statement best describes sentinel value -99's role for missing values?

• A. It indicates missing
• B. It indicates nothingness
• C. It indicates a real measurement
• D. It indicates zero value

Answer: (B)

Sentinel values act as placeholders to mark missing or unavailable data. When a dataset uses -99, that entry isn’t a real measurement; it’s a signal that the actual value is missing. In other words, it represents nothing recorded in that field, rather than a true measured value or zero. This distinction matters because downstream processes should treat -99 as missing data and handle it accordingly (e.g., ignore, impute, or flag), not as a legitimate numeric reading. So describing -99 as indicating nothingness best captures its role as a marker for missing data.