Question

Question 3: Consider a set of points, where most points are in regions of low density, but a few points are in regions of high density. If we define an anomaly as a point in a region of low density, then most points will be classified as anomalies. Is this an appropriate use of the density- based definition of an anomaly or should the definition be modified in some way?

Answer 1

Basically Anomaly means Abnormality. Anomalies are specific patterns in properties that do not match with the existing well-defined behaviour of the object patterns and also the associated properties.

Here we are discussing a point in a density region, so we have to consider the phenomena of Point Anomalies. Thus we will consider a single object and compare its properties with that of the surroundings.

Here if an observation lies in a very low-density region, we call it an anomaly or a novelty since it is the least probable dataset. Also what is considered normal now, can't be normal in the future. Thus when most of the observation points are falling in the low-density region, it is more likely to start showing normal behaviour and thus those points can't be regarded as Anomalies anymore. In that situation the previous high-density region will be the new anomolous region.