1. DataReportal: Internet users in the world 2020 | Statista. Statista GmbH, October 2020 (2022). https://www.statista.com/statistics/617136/digital-population-worldwide/
2. Newzoo: Smartphone users 2020 | Statista. Statista GmbH (2020). https://www.statista.com/statistics/330695/number-of-smartphone-users-worldwide/
3. App Annie; TechCrunch: Annual number of mobile app downloads worldwide 2020 | Statista. Statista, September 2020 (2020). https://www.statista.com/statistics/271644/worldwide-free-and-paid-mobile-app-store-downloads/
4. Lecture Notes in Computer Science;A Poniszewska-Maranda,2016
5. Kitchenham, B., Brereton, O.P., Budgen, D., Turner, M., Bailey, J., Linkman, S.: Systematic literature reviews in software engineering - a systematic literature review. Inf. Softw. Technol. 51, 7–15 (2009)