Zawacki-Richter, O., E. M. Baecker, and S. Vogt. “Review of Distance Education Research (2000 to 2008): Analysis of Research Areas, Methods, and Authorship Patterns”. The International Review of Research in Open and Distributed Learning, Vol. 10, no. 6, Dec. 2009, pp. 21-50, doi:10.19173/irrodl.v10i6.741.