- https://blog.edx.org/optimal-video-length-student-engagement/?track=blog
- https://www.wsj.com/articles/an-early-report-card-on-massive-open-online-courses-1381266504?tesla=y
- https://cacm.acm.org/news/168670-an-early-report-card-on-massive-open-online-courses/fulltext
- http://www.pgbovine.net/publications/edX-MOOC-in-video-dropouts-peaks_LAS-2014.pdf
- https://wistia.com/blog/optimal-video-length
- https://www.qualitymatters.org/qa-resources/resource-center/articles-resources/research-video-length
- http://up.csail.mit.edu/other-pubs/las2014-pguo-engagement.pdf