1. Nelson, R.: The top mobile apps, games, and publishers of Q1 2018: Sensor Tower’s Data Digest (2018).
https://sensortower.com/blog/top-apps-games-publishers-q1-2018
2. Anderson, J.R.: Cognitive Psychology and its Implications. Macmillan, London
3. Leading countries based on number of Instagram users as of October 2018 (2005).
https://www.statista.com/statistics/578364/countries-with-most-instagram-users/
4. Distribution of Instagram users worldwide as of October 2018, by age and gender.
https://www.statista.com/statistics/248769/age-distribution-of-worldwide-instagram-users/
5. People spend almost as much time on Instagram as they do on Facebook (2018).
https://www.recode.net/2018/6/25/17501224/instagram-facebook-snapchat-time-spent-growth-data