This report describes a pilot Environmental Sustainability Index, unveiled in 2001, which offers a detailed assessment of dozens of variables that influence the environmental health of economies. Its creators released rankings of 122 countries based on 67 separate variables, ranging from sulphur dioxide in the air to corruption. They devised 22 "core" indicators for the ESI, made up of those variables, which they weighted equally for the purpose of the country rankings. These range from eco-efficiency, to population stress, to the responsiveness of the private sector. They found that the indicators clump together naturally into five broad areas: environmental systems, reducing environmental stresses, reducing human vulnerability, social and institutional capacity, and global stewardship.