Peer groups were assigned by dividing the countries of the index into five equal groups, sorted by the GDP per capita. The peer group ESI is the Average ESI score for that group. Please see page 2 of Annex 5 (Country Profiles) of the ESI 2002 report for further details. Annex 5 can be downloaded at http://sedac.ciesin.columbia.edu/es/esi/archive.html.