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Our Methods

Our Methods

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.
The two objectives that provide the overarching structure of the 2014 EPI are Environmental Health and Ecosystem Vitality. Environmental Health measures the protection of human health from environmental harm. Ecosystem Vitality measures ecosystem protection and resource management. These two objectives are further divided into nine issue categories that span high-priority environmental policy issues, including air quality, forests, fisheries, and climate and energy, among others. The issue categories are extensive but not comprehensive (See: Data Gaps and Deficiencies, below). Underlying the nine issue categories are 20 indicators calculated from country-level data and statistics. Figure 1, below, illustrates the 2014 EPI framework and the objectives, issue categories, and indicators.
The 2014 EPI Framework includes 9 issues and 20 indicators. Access to Electricity is not included in the figure because it is not used to calculate country scores. Click on the interactive figure above to explore the EPI framework.

Calculating the EPI begins with transforming raw datasets to standardized, comparable performance indicators. Doing so requires standardizing raw values according to population, gross domestic product, or other denominators, which makes data comparable across countries. It can also involve applying statistical transformations, such as inversions or logarithmic transformations.

The transformed data are then used to calculate performance indicators. EPI indicators use a “proximity-to-target” methodology, which assesses how close a particular country is to an identified policy target. That target, a high performance benchmark, is defined primarily by international or national policy goals or established scientific thresholds. For example, the benchmarks for protected areas are determined through international policy targets established by the Convention on Biological Diversity (CBD)

Scores are then converted to a scale of 0 to 100 by simple arithmetic calculation, with 0 being the farthest from the target (worst observed value) and 100 being closest to the target (best observed value). See Figure 1 below. In this way, scores convey similar meaning across indicators, policy issues, and the overall EPI. 


Figure 1. Illustration of proximity-to-target method used to calculate performance indicators in the EPI.

Each indicator is weighted within each policy issue to create a single policy issue score. These weightings are generally set according to the quality of the underlying dataset, as well as the relevance or fit of the indicator to assess the policy issue. If the underlying global data for a particular indicator is less reliable or relevant than others in the policy issue, it will be weighted less heavily. For example, the trends in carbon intensity indicators in the Climate and Energy category are weighted according to which indicator is more pertinent based on a country’s economic development and policy obligations with respect to climate change mitigation. Policy issues and the overall objectives are similarly weighted to achieve a single value, the EPI score, for each country. 

→ The complete weightings used for each indicator, issue, and objective can be downloaded here.

For a more detailed explanation of the process used to create the EPI more generally, see Measuring Progress: A Practical Guide from the Developers of the Environmental Performance Index (EPI).

Penalties
 

The 2014 EPI penalizes the reporting country when experts or statistical analysis deem nationally reported data inadequate for performance evaluation purposes. These penalties were only given in two issues: Fisheries and Agriculture.

For example, if a country reported stock data to the Food and Agriculture Organization (FAO) that fisheries experts determine inadequate, the country was given the lowest average score for the given year — for both the Fish Stocks and Coastal Fishing Pressure indicators.

Comparability Across EPI releases and “Back-casted” Scores and Trends
 

The 2014 EPI website provides back-casted indicator scores wherever logical. The term “back-casted” refers to the application of the 2014 EPI framework, indicators, and aggregation method to historic data, starting from year 2002. In this way, countries can see how their performance from year to year may have changed on each indicator and what their scores and ranks would have been in years past. Not every indicator in the 2014 EPI lends itself to back-casted or trend calculations. The Change in Forest Cover indicator, for example, is already a measure of change, as it represents a calculation of net forest loss and gain from 2000 to 2012. Additionally, because the 2014 EPI presents all indicators in the Climate and Energy category as trends, back-casted scores or trend calculations were not relevant.

Wherever possible, the trend calculations for all other indicators are presented as roughly a 10-year percent difference in performance (e.g. 10 percent improvement), from 2002 levels to 2012, the latest year of data available for most indicators. Countries that demonstrate greater than a 100-percent improvement from 2002 scores are capped at 100 percent. These trends are presented on each country profile page website and downloadable data spreadsheets

Selection Criteria for Data in the EPI 
 

Relevance: The indicator tracks the environmental issue in a manner that is applicable to countries under a wide range of circumstances.

Performance orientation: The indicator provides empirical data on ambient conditions or on-the-ground results for the issue of concern, or it is a “best available data” proxy for such outcome measures.

Established scientific methodology: The indicator is based on peer reviewed scientific data or data from the United Nations or other institutions charged with data collection.

Data quality: The data represent the best measure available. All potential datasets are reviewed for quality and verifiability. Those that do not meet baseline quality standards are discarded.

Time series availability: The data have been consistently measured across time, and there are ongoing efforts to continue consistent measurement in the future.

Completeness: The dataset needs to have adequate global and temporal coverage to be considered.

Data Gaps and Deficiencies 
 

After more than 15 years of work on environmental performance measurement and six iterations of the EPI, global data are still lacking on a number of key environmental issues. These include, but are not limited to:

  • Freshwater quality
  • Toxic chemical exposures
  • Municipal solid waste management
  • Nuclear safety
  • Wetlands loss
  • Agricultural soil quality and degradation
  • Recycling rates
  • Adaptation, vulnerability, and resiliency to climate change
  • Desertification

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.