I have been using Anki SRS flashcard tool for 3 years to learn Spanish and some technical terms. Lots of data was accumulated which I am now analyzing:
GitHub - ran88dom99/Flashcards-as-Cognitive-Test: In depth analysis of the data Anki records for, possibly, cognitive testing. Also teaches users about learning and allows them to experiment with and optimize their own learning process. Encourages via gamification too.
Heights based on percent of cards added that period. Separate histograms for each subject. I just think its pretty.
Following plot shows that I got overenthusiastic in adding new decks and have yet to review most of them. Also the overenthusiasm happened after good additions and then faded.
Histogram of reviews (answering a card), colored by subject. Shows I have had some slack periods of which the biggest is happening right now. Studying of subjects other than Spanish has been decreasing pretty much from the start. This probably just means I have learned the material I started.