Données statistiques.

Environmental data report United Nations Environment Programme 1987 Food Review United States Department of Agriculture, Economic Research Service Year not listed International financial statistics Monetary Fund, International 1997 Journal of public economics Author not listed Year not listed National Institute economic review Author not listed Year not listed OECD economic surveys Author not listed 1975 Oxford review of economic policy Author not listed 1985 Review of world economics IfW 2003 The journal of economic perspectives Author not listed 1987 The World Bank research observer Author not listed 1986