To make the 25 indicators comparable, each metric was converted to a proximity-to-target-measure with a range of 0 to 100. Prior to this step, we examined the distribution of each indicator and transformed some indicators logarithmically to keep extreme values from skewing the aggregations. However, where there was reason to believe that the extreme values were “outliers” rather than the result of a skewed distribution, they were adjusted to make them equal to the value of the 5th percentile, a recognized statistical technique called winsorization.
A second decision concerned the treatment of countries that exceeded the long-term performance or sustainability target. To avoid rewarding “over-performance,” no indicator values above the long-term target were used. In the few cases where a country did better than the target, the value was reset so that it was equal to the target. Once those two adjustments were made, a simple arithmetic transformation was undertaken: the observed values were placed onto a zero to 100 scale where 100 corresponds to the target and zero to the worst observed value.
Aggregation is an area of inescapable methodological controversy. While the field of composite index construction has become a well-recognized subset of statistical analysis, there is no clear consensus on how best to construct composite indices. Various aggregation methods exist, and the choice of an appropriate method depends on the purpose of the composite indicator as well as the nature of the subject being measured.
To help identify appropriate groupings and weights for each indicator, we carried out a principal component analysis (PCA). Most categories did not have clear referents in the PCA results. Absent a PCA-derived basis for weighting the indicators, equal weights were used with some refinements determined by the EPI team with expert guidance.
The Environmental Health and Ecosystem Vitality subcategories each represent 50% of the total EPI score. This equal division of the EPI into issues related to (1) humans and (2) nature is not a matter of science but rather policy judgment. But this even weighting of the two overarching objectives of environmental policy reflects a broad-based institution – and this choice (used in the 2006 Pilot EPI) has not been generally criticized. Indeed, for every “deep ecologist” who favors more weight being placed on Ecosystem Vitality, there is a “humans first” environmental policymaker who prefers that the tilt go the other way.
Within the Environmental Health subcategory, the Environmental Burden of Disease (DALY) indicator is weighted 50% and accordingly contributes 25% of the overall EPI score, because it is widely regarded to be the most comprehensive and carefully-defined available measure of environmental health burdens. The effects of Water and Air Pollution on human health comprise the remainder of the Environmental Health subcategory and are each allocated a quarter of the total score for Environmental Health, reflecting a widespread policy consensus.
The two water-related indicators (Adequate Sanitation and Drinking Water) are equally weighted. Urban Particulates and Indoor Air Pollution receive equal weights, and double the weight given to the effects of ground-level Local Ozone on human health. Urban Particulates and Indoor Air are widely acknowledged by the United Nations Environment Programme (UNEP), World Health Organization (WHO), and United Nations Children’s Fund (UNICEF) as excellent indicators of the burden of air pollution on human health. There is, however, a growing literature that suggests a link between ozone exposure and human health. Our human-exposure-related ozone metric builds on ozone exposure modeled by Denise Mauzerall and her colleagues on the global chemical transport Model of Ozone and Related Tracers, version 2 (MOZART-2). Because this indicator is experimental, we give it half the weight of those with known reliability.
Within the Ecosystem Vitality subcategory, the Climate Change indicator carries 50% of the subcategory’s weight. The Air Pollution indicator is weighted to 2.5% of the subcategory total, due to the statistical variance of the datasets and the understanding that policymakers find water issues more fundamental than air pollution to ecosystem vitality. The remaining indicators: Water, Biodiversity, and Productive Natural Resources, are each evenly weighted to cover the remaining 22.5% of the subcategory.
Good Morning, i can obtain the PDF version of EPI report. Where I can Download the report? Thanks