8Chyung,Y.,Winiecki,D.& Fenner,J.(1998).A Case Study:Increase Enrolment by Reducing Dropout Rates in Adult Distance Education[A].Distance Learning98 Proceedings of the Annual Conference on Distance Teaching and Learing,Madison,WI,August 5-7.Two Different Distance Education Courses[C].Retrieved on December 21,2005 at http://www.irrodl.org/content/v5.2/pierrakeas-research.html
9More,M.G.& Kearsley,G.(1996).Distance Education:A systems View[M].Belmont,CA:Wadsworh.
10Pierrakeas,C.(2004).Comparative Study of Dropout rates and Causes for Two Different Distance Education Courses[OL].Retrieved on December 21,2005 at http://www.irrodl.org/content/v5.2/pierrakeas-research.html