The 2008 EPI builds on the best environmental data available, but remains seriously constrained by a lack of both quality and quantity in data sources. About 90 countries cannot be included in the EPI because data are not available in one of the six policy categories. Many critical issues also lack reliable measures. The 2008 EPI covers 149 of a possible 238 countries.
Due to a lack of data, limited country coverage, methodological inconsistencies, or otherwise poor-quality metrics, a number of relevant issues that are considered to be policy relevant and scientifically important are not reflected in the EPI. These gaps include: