Indicators were sought to cover the full spectrum of issues underlying each of the major policy categories identified. To ensure the use of the best suited metrics, the following indicator selection criteria were applied:
Relevance: The indicator clearly tracks the environmental issue of concern in a way that is relevant to countries under a wide range of circumstances.
Performance orientation: The indicator tracks ambient conditions or on-the-ground results (or is a “best available data” proxy for such outcome measures).
Transparency: The indicator provides a clear baseline measurement, has the ability to track changes over time, and is transparent with regard to data sources and methods.
Data quality: The data used by the indicator should meet basic quality requirements and represent the best measure available.
The EPI builds on a set of carefully chosen policy targets (see last column of Table 2). Measuring success against these targets provides useful information about country-specific conditions and policy results, as well as areas in need of increased attention and resources. A proximity-to-target measure helps to clarify comparative rankings, demonstrate which countries are leading or lagging in each area, and whether (as a global aggregate) the world is on a sustainable trajectory.
Whenever possible our targets are based on international treaties and agreements. For issues with no international agreements, we looked next to environmental and public health standards developed by international organizations and national governments, the scientific literature, and finally, expert opinion from around the world. Only a few of the indicators have explicit consensus targets established at a global scale. This suggests that there is also a need for the international and national policy communities to be clearer about the long-term goals of environmental policies set at all levels. International agreements are often based on compromises, however, and targets derived from them do not necessarily reflect environmental performance required for full sustainability.
