Unlabeled data contains instances without assigned target labels or annotations. It is central to unsupervised outlier detection, where patterns and deviations are extracted from the overall data distribution. In semisupervised learning, unlabeled records complement a smaller labeled set, although the distribution may not always predict the target reliably. section 15.4 section 1.7
Practical implications include:
- Outlier detectors can flag records for manual labeling, including records just below a decision threshold. section 15.4
- The unlabeled majority can reveal useful distributional structure, especially when that structure is fundamental to outlier detection. section 15.4
- A small labeled subset may be insufficient for a reliable classifier when data volume is low or smoothness and clustering assumptions fail. section 15.4
From detector scores to labels
A dataset with 100,000 rows may produce 200 flagged records. Manually reviewing those records and spot-checking 100 unflagged rows creates approximately 300 labeled examples, which may still be too few for a dependable classifier. section 15.4



