The determination of optimal cluster number by Silhouette index at clustering of the European Union member countries and candidate Turkey by waste indicators

Abstract

This study aims to identify cluster structure of European Union (EU) Member countries and Candidate Turkey in terms of environmental waste indicators and to determine the other member countries which are classified in the same cluster with Turkey. Hierarchical and non-hierarchical clustering methods were used to determine clusters of 28 member countries and Turkey according to the total 8 environmental waste indicators. The optimal cluster number and the best method were identified with the silhouette index which is a cluster validity index. The results from the cluster analysis using the hierarchical and non-hierarchical methods showed that there are six clusters according to the environmental waste indicators of EU countries and Turkey. The average Silhouette index shows that the k-means gives more valid results than the ward. According to the Silhouette index obtained by k-means method, Turkey has been found to be classified in the same cluster with 50% of the EU countries such as Poland, Hungary, and Latvia etc.