1. Environmental Policy Performance Indicators;Adriaanse,1993
2. Bagnasco, G., 2010. Grandi città in crisi sul fronte ambientale. Available from: http://www.ilsole24ore.com/art/notizie/2010-10-15/grandi-citta-grigie-210438.shtml (accessed May 2011).
3. Bandura, R., 2008. A Survey of Composite Indices Measuring Country Performance (update). A UNDP/ODS Working Paper. Available from: http://www.undp.org/developmentstudies/docs/indices_2008_bandura.pdf (accessed May 2009).
4. BirdLife, 2009. Wild Bird Indices: tracking trends in the condition of habitats. Available from: http://www.birdlife.org/action/science/indicators/common_birds.html (accessed June 2009).
5. Greened national statistical and modelling procedures;Brouwer;International Journal of Sustainable Development,1999