1. C. Stephenson J. Gal-Ezer B. Haberman A. Verno 2005 http://www.csta.acm.org/Publications/White_Paper07_06.pdf
2. 2006 http://research.microsoft.com/towards2020science/background_overview.htm
3. http://www.eurydice.org/ressources/eurydice/pdf/0_integral/048EN.pdf
4. 2007 http://www.unescobkk.org/index.php?id=657
5. O. E. Taulbee 2003 http://www.cra.org/statistics/