Commentary: Classification and cluster analysis

One of the most basic abilities of living creatures involves the grouping of similar objects to produce a classification. As well as being a basic human conceptual activity, classification is also fundamental to most branches of science. In chemistry, for example, the classification of the elements in the periodic table has had a profound impact on the understanding of the structure of the atom. Classification in medicine is equally important, with the classification of diseases being of primary concern as the basis for investigations of aetiology and treatment. Statistical techniques for classification are essentially of two types. Members of the first type are used to construct a (hopefully) sensible and informative classification of an initially unclassified set of data; these are known as cluster analysis methods. The information on which the derived classification is based is generally …