| 1993-2004 (Tallent-Runnels [10] ) | 2000-2008 (Zawacki [12] ) | 2009-2018 (Martin [11] ) |
Most number of studies | •Course environment •Learner outcomes | •Interaction and communities of learning •Instructional design •Learner characteristics | •Engagement •Learner characteristics •Evaluation and quality assurance |
Lowest number of studies | •Learner characteristics •Institutional and administrative factors | •Management and organization •Research methods in DE and knowledge transfer •Globalization of education and cross-cultural aspects | •Course design and development •Leadership, policy, and management •Instructor characteristics |