The Use and Misuse of Composite Environmental Indices

Composite indices have been widely used to rank the environmental performance of nations. Such environmental indices can be useful in communicating complex information as a single value and have the potential to generate political and media awareness of environmental issues. However, indices that are poorly constructed can hinder efforts to identify environmental failings. Here, we provide a critical review of the theoretical and methodological foundations of environmental indices to enhance our understanding of the accuracy and applicability of such indices. In the present study we classify existing indices according to ranking goal, measurement components, and weighting methods. Using New Zealand and Niger as case studies, we examine correlations between ranks in ten national level indices to outline how measurement components and the goal of ranking itself may provide a more, or less, optimistic view of the state of a countrys environment. Our results suggest that environmental indices that include human health, socioeconomic, and policy indicators (such as human access to sanitation and clean drinking water) are positively correlated with each other, and that those excluding human health, socioeconomic, and policy indicators are also positively correlated with each other, while these two types of environmental indices are negatively correlated to each other. Our results demonstrate that the inclusion of indicators that do not relate to the actual state of natural environments can confound results. When choosing an existing environmental index - or developing a new one - it is important to assess whether the ranking goal and the included indicators are appropriate. This is important because the inclusion of confounding indicators in environmental indices may misrepresent the actual state of natural environments.