Outlier Detection (2): Proximity-Based Methods
- An object is an outlier if the nearest neighbors of the object are far away, i.e., the proximity of the object is significantly deviates from the proximity of most of the other objects in the same data set
- The effectiveness of proximity-based methods highly relies on the proximity measure.
- In some applications, proximity or distance measures cannot be obtained easily.
- Often have a difficulty in finding a group of outliers which stay close to each other
- Two major types of proximity-based outlier detection
- Distance-based vs. density-based
- Example (right figure): Model the proximity of an object using its 3 nearest neighbors
- Objects in region R are substantially different from other objects in the data set.
- Thus the objects in R are outliers