Clustering of population pyramids using Mallows' L2 distance
In many real situations, data are collected/presented as histograms. Such examples are population pyramids, which present the age distribution of a population by gender for a particular country. The objective of this paper is to partition countries into homogenous groups according to the similarity of the shape of the population pyramids in each particular year and to observe the time-trend. We use a Mallows' L2 distance for this purpose. A case study on East European countries in the period 1995–2015 is presented. The results reflect that the countries are becoming more and more similar and follow a pattern of aging populations. For the majority of countries, this process started long before 1990, for Kosovo, Albania and Macedonia it started after 1990.