The 2008 EPI offers a composite index of current national environmental protection efforts. Recognizing that on-the-ground conditions are the ultimate gauge of environmental performance, the EPI focuses on measurable outcomes that can be linked to policy targets and tracked over time.
The EPI builds on measures relevant to two core objectives:- reducing environmental stresses to human health (the Environmental Health objective); and
- protecting ecosystems and natural resources (the Ecosystem Vitality objective).
The quantitative metrics underlying the 2008 EPI encompass 25 indicators chosen through: a broad-based review of the environmental science literature; in-depth consultation with a group of scientific advisors in each policy category; the evidence from the Millennium Ecosystem Assessment, the Intergovernmental Panel on Climate Change, the Global Environmental Outlook-4, and other assessments; environmental policy debates surrounding multilateral environmental agreements; and expert judgment. Each indicator builds on a foundation either in environmental health or ecological science.
Some of these metrics track the underlying concept closely. Others are “proxy” variables that imperfectly reflect the theoretical focus. The EPI uses the best available global data. The 25 indicators each represent core elements of the environmental policy challenge.
For each indicator, a relevant long-term public health or ecosystem sustainability goal is identified. These targets are drawn from 1) treaties or other internationally agreed upon goals; 2) standards set by international organizations; 3) leading national regulatory requirements; or the 4) prevailing scientific consensus. The indicators serve as a gauge of long-term environmental policy success. For each country and each indicator, a proximity-to-target value is calculated based on the distance from a country’s current results to the policy target.
In calculating EPI scores, we average around isolated data gaps. But countries with more than a few missing data values (preventing any of our category scores from being calculated) are dropped from the Index. Our data matrix covers 149 countries for which an EPI can be calculated across the 25 indicators. Data gaps mean that another 90 or so countries cannot be ranked in the 2008 EPI.
Using the 25 indicators, scores are calculated at three levels of aggregation (see Figure 1).
- First, building on two to eight underlying indicators (each representing a data set), we calculate scores for each of the six core policy categories – Environmental Health, Air Quality, Water Resources, Biodiversity and Habitat, Productive Natural Resources, and Climate Change. In some cases, subcategories are also tracked. The weight given to each indicator varies as shown in Table 2. This level of aggregation permits countries to track their relative performance within these well-established policy areas – or at the disaggregated indicator level.
- Second, the Environmental Health subcategories and the Ecosystem Vitality categories are aggregated with weights allocated as shown in Figure 1.
- Finally, the overall Environmental Performance Index is calculated, based on the arithmetic mean of the two broad objective scores. The logic for the weightings each subcategories and indicators is discussed below.
