1. http://www.sacscoc.org/pdf/081705/distance%20education.pdf
2. 2007 http://www.sloan-c.org/publications/survey/survey07.asp
3. The virtual university: Toward an internet paradigm?;Carswell;ACM SIGCSE Bull.,1998
4. http://www.sloan-c.org/publications/survey/pdf/making_the_grade.pdf