Failed or delisted observations are missing
Typical symptoms
- The sample only includes current winners
- Older periods show suspiciously strong quality
- Universe construction is not documented
Likely causes
- Current constituents were applied backward
- Unavailable or failed observations were removed
- Data coverage limitations were not disclosed
Checks
- Rebuild the universe as of each historical date
- Count missing observations by period
- Compare current-only and historical-universe results
Resolution path
- Use historical membership where available
- Disclose coverage gaps
- Treat current-only analysis as limited exploratory evidence
Related terms: survivorship, universe, delisting, coverage
