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2. Allen, I.E. and Seaman, J. (2004), Entering the Mainstream: The Quality and Extent of Online Education in the United States, 2003 and 2004, Sloan Consortium, Needham, MA, available at: www.sloan‐c.org/publications/survey/index.asp.
3. Allen, I.E. and Seaman, J. (2006), Making the Grade: Online Education in the United States, 2006, Sloan Consortium, Needham, MA, available at: www.sloan‐c.org/publications/survey/index.asp.
4. Nation Center for Educational Statistics (2005), Digest of Education Statistics 2005, available at: http://nces.ed.gov/programs/digest/d05/tables/dt05_170.asp.
5. Allen, I.E. and Seaman, J. (2005), Growing by Degrees: Online Education in the United States, 2005, Sloan Consortium, Needham, MA, available at: www.sloan‐c.org/publications/survey/index.asp.