1. Department of Informatics and Telecommunications, University of Ioannina, 47100 Arta, Greece
2. Turku Research Institute for Learning Analytics, University of Turku, 20014 Turku, Finland
3. School of Natural Sciences, University of Patras, 26504 Patras, Greece
4. School of Humanities, Hellenic Open University, 26335 Patras, Greece