Tier A Statistical anomaly
An entity stands out as a numerical outlier inside a single dataset.
Detectors in this tier
- Benford's Law deviation. First-digit distribution of contribution amounts deviates from the calibrated NV baseline (Tam Cho & Gaines 2007).
- Donor-base concentration (HHI). Single-donor share of a recipient's contribution base above the U.S. DOJ antitrust 'highly concentrated' threshold of 0.25.
- Isolation Forest outlier. Per-entity feature vector lies far from the bulk of its peers (Liu, Ting, Zhou 2008).
What it means
An entity is statistically unusual relative to its peers. By itself this is not evidence of wrongdoing — outliers exist in every distribution. Tier A is the starting point: an entity worth looking at more closely.