1. World Tourism Organization,Indicators of sustainable development for tourism destinations: a guidebook(World Tourism Organization, Madrid (2004)
2. http://www.odi.org/sites/odi.org.uk/files/odi-assets/publications-opinion-files/2861.pdf
3. http://www.ahs.uwaterloo.ca/rec/pdf/inttrends.pdf
4. www.twnside.org.sg/title/tourism.doc
5. http://hss.ulb.uni-bonn.de/2008/1288/1288.pdf