What Clusters Are Generated by Normal Mixtures

Model based cluster analysis is often carried out by estimation of the parameters of a normal mixture. But mixture components do not necessarily reflect the idea of a “cluster”. I discuss how to formalize the concept of “clusters” w.r.t. probability distributions on the real line by means of fixed point clusters, i.e., sets that do not contain any outlier and with respect to which the rest of the real line consists of outliers. The concept is applied to some normal mixtures