Fueled by advances in information technology, data-driven decisionmaking has transformed every corner of society, from business to biology. In the policy domain, quantitative performance metrics have reshaped decisionmaking processes in many arenas, including economics, health care, and education. The 2008 Environmental Performance Index (EPI) brings a similar data- driven, fact-based empirical approach to environmental protection and global sustainability.

Policymakers in the environmental field have begun to recognize the importance of incorporating analytically rigorous foundations into their decisionmaking. However, while policymakers are calling for increased intellectual rigor in environmental planning, large data gaps and a lack of time-series data still hamper efforts to track many environmental issues, spot emerging problems, assess policy options, and gauge effectiveness. The EPI seeks to fill these gaps and, more broadly, to draw attention to the value of accurate data and sound analysis as the basis for environmental policymaking.

The EPI focuses on two overarching environmental objectives:

• reducing environmental stresses to human health;
  
• promoting ecosystem vitality and sound natural resource management

These broad goals also reflect the policy priorities of environmental authorities around the world and the international community's intent in adopting Goal 7 of the Millennium Development Goals (MDGs), to "ensure environmental sustainability." The two overarching objectives are gauged using 25 performance indicators tracked in six well-established policy categories, which are then combined to create a final score.

The 2008 EPI deploys a proximity-to-target methodology, which quantitatively tracks national performance on a core set of environmental policy goals for which every government can be - and should be - held accountable. By identifying specific targets and measuring the distance between the target and current national achievement, the EPI provides both an empirical foundation for policy analysis and a context for evaluating performance. Issue-by-issue analysis and aggregate rankings facilitate cross-country comparisons both globally and within relevant peer groups such as geography or economy.

It must be emphasized that the EPI's real value lies not in the numerical rankings, but rather in careful analysis of the underlying data and performance metrics. The results are displayed in numerous ways: by issue, policy category, peer group, and country. This format allows for identification of leaders and laggards, highlights best policy practices for each issue, and identifies priorities for action for each country. More generally, the EPI provides a powerful tool for steering environmental investments, refining policy choices, optimizing the impact of limited financial resources, and understanding the determinants of policy results.

Policy Conclusions Environmental decisionmaking can and should be made more data-driven and rigorous. A more fact-based and empirical approach to policymaking promises systematically better results. Notwithstanding data gaps and methodological limitations, the EPI demonstrates that environmental results can be tracked quantitatively, facilitating more refined policy analysis. To address these gaps, policymakers should invest in collecting additional data and tracking a core set of indicators over time. They must also set clear policy targets and incorporate indicators and reporting into policy formation, and shift toward more analytically rigorous environmental protection efforts at the global, regional, national, state/provincial, local, and corporate scales. Environmental challenges come in several forms which vary with wealth and development. Some issues arise as a function of economic activity and its resource and pollution impacts, such that developed and industrializing countries face the most severe harms. Other threats derive from poverty or a lack of basic environmental amenities, such as access to safe drinking water and basic sanitation. These issues affect primarily developing nations. Wealth correlates highly with EPI scores and particularly with environmental health results. But at every level of development, some countries achieve results that exceed their income-group peers while others fail to keep up. Statistical analysis suggests that in many cases good governance contributes to better environmental outcomes. The EPI uses the best available global datasets on environmental performance, but the overall data quality and availability is alarmingly poor. The absence of broadly-collected and methodologically-consistent indicators for even basic concerns such as water quality - and the complete lack of time-series data for most countries - hampers efforts to shift pollution control and natural resource management onto more empirical foundations. The 2008 EPI relied on a team of scientific advisors and expert peer reviewers to identify the most appropriate indicators in each policy category, and in some cases to assist in processing the data, making this a truly collaborative effort with strong scientific underpinnings. Still, the EPI represents a work in progress, and comments and criticisms are welcome. It is intended not only to inform, but also to stimulate debate on defining the appropriate metrics and methodologies for evaluating environmental performance. As existing conceptual, methodological, and data challenges are overcome, better metrics will emerge - and a more refined EPI will be possible.

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