Exploring compositional data with the coda-dendrogram

Abstract

Within the special geometry of the simplex, the sample space of compositional data, compositional orthonormal coordinates allow the application of any multi- variate statistical approach. The search for meaningful coordinates has suggested balances (between two groups of parts)|based on a sequential binary partition of a D-part composition|and a representation in form of a CoDa-dendrogram. Projected samples are represented in a dendrogram-like graph showing: (a) the way of grouping parts; (b) the explanatory role of subcompositions generated in the partition process; (c) the decomposition of the variance; (d) the center and quantiles of each balance. The representation is useful for the interpretation of balances and to describe the sample in a single diagram despite the number of parts. Also, samples of two or more populations, as well as several samples from the same population, can be represented in the same graph, as long as they have the same parts registered. The approach is illustrated by an example of food consumption in Europe.