Cluster analysis to validate the sustainability label of stock indices: An analysis of the inclusion and exclusion processes in terms of size and ESG ratings

Sustainability stock indices play an important role in guiding socially responsible funds to their constituents. Thus, to find out whether the term sustainability is more than just a label, we analyze the inclusion and exclusion criteria applied by sustainability indices, and we compare them with those applied by conventional indices. We analyze the level of sustainability and size of the companies included in and excluded from five sustainability indices compared to a control group of 11 conventional indices. Our results show that the level of sustainability influences the inclusion process and, to a lesser extent, the exclusion process of the five FTSE4Good indices. However, we find similar results for several conventional indices. In addition, the size criterion dominates the sustainability criterion in the inclusion and exclusion processes of sustainability indices like in conventional indices. Further, we use different cluster algorithms to determine that the inclusion and exclusion processes of four of the five sustainability indices are different from those of the conventional indices. Our results validate the use of the “sustainability” label for four of five sustainability indices but also show that further differentiation between sustainability and conventional indices is needed. •Size predominates over ESG scores in the inclusion/exclusion of sustainable indices•Cluster analysis detects differences among sustainability and conventional indices•Cluster analysis as a method for validating the index classifications•Further differentiation is needed among sustainability and conventional indices