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Why Measurement Matters

The Environmental Performance Index (EPI) was born out of a recognition that environmental policymaking lacked scientific, quantitative rigor. While Millenium Development Goal 7 – to ensure environmental sustainability – first placed the notion of sustainable development on the global policy agenda, that particular goal lacked relevant or dependable metrics. To address this gap, the Yale Center for Environmental Law & Policy (YCELP) and the Center for International Earth Science Information Network (CIESIN) at Columbia University partnered with the World Economic Forum to develop indices assessing environmental sustainability (the Environmental Sustainability Index) and environmental performance (the EPI). Both were created with an eye toward shaping data-driven environmental policymaking.

The need for better data and metrics to guide decisionmaking could not be more urgent.

Effective environmental policy is burdened by two related hurdles, both of which are lowered by better measurement. First, environmental policy debates are subject to deep divisions over the best way forward. Second, substantial uncertainty surrounding the nature of environmental problems makes significant action and allocation of resources difficult to justify. Good environmental measurement can inject more objectivity in environmental policy debates, reducing disagreement on the scope of problems and focusing it instead on solutions.

Robust measurement also gives policymakers a foundation from which to promote environmental policy. When policymakers use data to reduce uncertainty, they can advance policy objectives with more than educated guesses or hunches. The trend of using data, and increasingly “big data,” is becoming a common business and government practice. Large corporate entities collect consumer information to better target advertisement campaigns. Government leaders, like former New York City Mayor Michael Bloomberg, base management decisions on data as diverse as the number of heart attacks and noise complaints.

The business sector has long understood that data can make the invisible visible, and it has used metrics to improve performance. A business collects data and will make changes depending on its sales figures, for example. Environmental indicators have likewise proved useful tools in helping policymakers more efficiently allocate scarce resources. As the time-tested mantra goes, “you can’t manage what you don’t measure.”

Measurement matters because it provides an essential tool to policymakers. It also matters because measurement highlights gaps in collective knowledge. Data on environmental problems is severely lacking across the globe. At the local, national, and international level, decisionmakers need better data. Indices like the EPI help direct attention to vital data gaps, which can help generate better data for the future.


The Environmental Performance Index (EPI) is constructed through the calculation and aggregation of 20 indicators reflecting national-level environmental data. These indicators are combined into nine issue categories, each of which fit under one of two overarching objectives. Click on "Learn More" to explore the complete methods.

Data Explorer

The EPI Data Explorer allows users to dynamically investigate global data: Compare environmental performance with GDP, population, land area, or other variables; create a chart that highlights all 178 ranked countries, only those in a specific region, or a custom-defined group. There's a lot more to the data than rankings, so dive in.