EPI FAQ

EPI FAQ

Question: 

How should I cite the EPI?

The suggested citation for the 2020 EPI:

Wendling, Z.A., Emerson, J.W., de Sherbinin, A., Esty, D.C., et al. (2020). 2020 Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy. epi.yale.edu

How was the 2020 EPI affected by the COVID-19 pandemic / Australia’s wildfires / burning of the Amazon?

Unfortunately, these events are too recent to be captured in the 2020 EPI. Most of our datasets were collected in 2018 or before; our Technical Appendix  provides precise details of temporal coverage for each indicator. Our data partners need time to collect, assemble, verify, and disseminate their datasets, and there is usually a lag between when data are measured and when they are available for use in the EPI. Developing global data systems that can provide frequent, up-to-date information on environmental conditions requires greater commitments and support from countries around the world.

Where can I find the data used in the EPI?

The data used in the calculations for the EPI are available on our downloads page.

Where do data for the EPI come from?

Data for the EPI come from international organizations, research institutions, academia, and government agencies. Most of our data are verified by a third party or produced from a data collection process that can be accessed and audited by a third party to confirm results. Generally, we do not accept data directly from governments themselves. Our Technical Appendix provides additional details on data sources for all variables used in the 2020 EPI.

Why did a country rise/drop since the last EPI?

A country’s current score in the 2020 EPI should not be compared to scores from previous versions of the Index. With every version of the EPI, we change the methodology and use new datasets to reflect the latest advances in science and metrics. These changes mean that scores calculated under the old methods are not comparable to the new scores.

In order to gauge how well a country performs over time, we recommend looking at individual country profiles. They show how a country scores using the most recent data and how those scores have changed over the past decade.

Can I assemble the releases of the EPI into a time series or panel dataset?

No. Because the underlying methodology and data change between versions of the EPI, it is not appropriate to assemble the scores from each release into a time series. If you wish to analyze longitudinal data on environmental performance, historic time series for many indicators are available on our downloads page.

Why don’t you backcast EPI scores?

Backcasting scores using the 2020 EPI methodology is infeasible for several reasons. As shown in our Technical Appendix, the underlying data series we use are asynchronous. Datasets have different beginning and end periods, some have several gaps in temporal coverage, and some have only a single year of observations. In order to produce a time series of the EPI, we would need to impute missing values for all of the underlying indicators over a common time period, which is highly problematic if not misleading. For example, we could try to estimate a linear trend or simply hold a value constant over missing years, but this would make it seem as if environmental performance was unresponsive to policy – or to any other explanatory factor – and mask any actual changes in outcomes.

For researchers interested in time series analysis, we recommend working with individual indicators or issue categories for which longitudinal observations are available, rather than the full EPI scores. Previous analyses have also used backcasted scores produced for the 2014 and 2016 versions of the EPI, available for download in our archives.

To give some reference for how performance changes over time, we also backcast a score using data approximately ten years prior to the most recent data, if available. We sometimes referred to these ten-year backcasts as the “baseline” scores. The scores based on the most recent year for which data are available are sometimes referred to as the “current” scores. For simplicity, we most often discuss the differences between the current and baseline scores as the ten-year change in performance. We describe further details about temporal coverage and backcasting in the online Technical Appendix.

Where can I find previous versions of the EPI?

Older versions of the EPI can be downloaded from the Socioeconomic Data and Applications Center (SEDAC).

Where is the EPI from 2019/2017/2015/2013/etc. ?

The EPI is released biennially in even-numbered years.

When will the next EPI be released?

The next EPI will be released in 2022. This website will be updated as the release draws closer.

Can I have permission to use the EPI for commercial purposes?

No. The 2020 EPI is released under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International LicenseNeither the 2020 EPI nor the data available on our downloads page may be used for commercial purposes. Our partners share data with us under certain restrictions, and the data usage agreements under which we operate prohibit the use of the EPI or derivative works in commercial products. Our data partners are listed in the data sources section of the Technical Appendix.

Can I have permission to use the EPI for educational, research, or other non-commercial purposes?

Yes. The 2020 EPI is released under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. You may use the 2020 EPI, including the scores, report, policymakers’ summary, and other material on this website, according to the terms of this license. Please email us if you would like to reproduce specific images.

How recent are the data from which the EPI is calculated?

The EPI always attempts to use the most recent data available for each indicator. Some data are more recent than others, and some data systems take several years to collect data on every country. The most recent year for each indicator is reported in the Technical Appendix.

How was a particular score calculated?

For a complete description of our methodology, please see the Technical Appendix.

What can a country do to improve its score in the EPI?

Specific policy recommendations are beyond the scope of our analysis. EPI rankings and scores allow for meaningful comparisons across peer countries. We encourage countries that aspire to become more sustainable to look to peer leaders for insights, lessons, and best practices that might be most appropriate for their own, individual challenges.

We do make three general policy recommendations: every country should improve data collection on environmental outcomes, support global data systems, and incorporate metrics and rigorous analysis into policymaking processes.

Why is there a missing score in the data?

EPI data may contain missing values for one of two reasons. First, while the EPI strives to find datasets that are comprehensive, not all data are available for every country. Second, sometimes a metric will be judged as immaterial in the calculation of the EPI, e.g., landlocked countries will not have scores for fisheries or marine protected areas. To learn more about country coverage and materiality, please see our Technical Appendix.

Why didn’t you use a certain dataset?

While there are more data available now than ever before, not all datasets are applicable to the EPI. For a description of our data selection process, please see Chapter 15 on Methodology in the report.

How should I cite previous versions of the EPI?

The suggested citations for previous versions of the EPI and the Environmental Sustainability Index (ESI) are

Wendling, Z. A., Emerson, J. W., Esty, D. C., Levy, M. A., de Sherbinin, A., et al. (2018). 2018 Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy. https://epi.yale.edu/

Hsu, A., Esty, D. C., de Sherbinin, A., Levy, M. A., et al. (2016). 2016 Environmental Performance Index: Global Metrics for the Environment. New Haven, CT: Yale Center for Environmental Law & Policy. https://epi2016.yale.edu/

Hsu, A., Emerson, J. W., Levy, M. A., de Sherbinin, A., Johnson, L., Malik, O. A., Schwartz, J. D., & Jaiteh, M. (2014). 2014 Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy. https://archive.epi.yale.edu/

Emerson, J. W., Hsu, A., Levy, M. A., de Sherbinin, A., Mara, V., Esty, D. C., & Jaiteh, M. (2012). 2012 Environmental Performance Index and Pilot Trend Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy.

Emerson, J. W., Esty, D. C., Levy, M. A., Kim, C. H., Mara, V., de Sherbinin, A., & Srebotnjak, T. (2010). 2010 Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy.

Esty, D. C., Levy, M. A., Kim, C. H., de Sherbinin, A., Srebotnjak, T., & Mara, V. (2008). 2008 Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy.

Esty, D. C., Levy, M. A., Srebotnjak, T., de Sherbinin, A., Kim, C. H., & Anderson, B. (2006). Pilot 2006 Environmental Performance Index. New Haven, CT: Yale Center for Environmental Law & Policy.

Esty, D. C., Levy, M. A., Srebotnjak, T., & de Sherbinin, A. (2005). 2005 Environmental Sustainability Index: Benchmarking National Environmental Stewardship. New Haven, CT: Yale Center for Environmental Law & Policy.

Esty, D. C., Levy, M. A., Granoff, I. M. E., & de Sherbinin, A. (2002). 2002 Environmental Sustainability Index. New Haven, CT: Yale Center for Environmental Law & Policy.

Esty, D. C. (2001). Toward data-driven environmentalism: the environmental sustainability index. Environmental Law Reporter News and Analysis, 31(5), 10603.

Esty, D. C., Levy, M. A., Granoff, I. M. E., & de Sherbinin, A. (2000). Pilot Environmental Sustainability Index. New Haven, CT: Yale Center for Environmental Law & Policy.

How is the EPI funded?

The EPI is funded through the generous support of the McCall-MacBain Foundation.