12.4 Proximity-Based Approaches

Given a set of objects in feature space, a distance measure can be used to quantify the similarity between objects. Intuitively, objects that are far from others can be regarded as outliers. Proximity-based approaches assume that the proximity of an outlier object to its nearest neighbors significantly deviates from the proximity of the object to most of the other objects in the data set.

There are two types of proximity-based outlier detection methods: distance-based and density-based methods. A distance-based outlier detection method consults the neighborhood of an object, which is defined by a given radius. An object is then considered an outlier if its neighborhood does not have enough other points. A density-based ...

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