Nikolova, Alexandra, Vladimir Georgiev, and Emanuela Mitreva. “Evaluation of Achievement Badges As a Gamification Method for Increasing Motivation in E-Learning”. Digital Presentation and Preservation of Cultural and Scientific Heritage 14 (September 5, 2024): 241–248. Accessed June 1, 2025. https://dipp.math.bas.bg/dipp/article/view/dipp.2024.14.22.