Memorization: optimizing flashcard review with spaced repetition
We often hear about how important it is to understand, to not just memorize information blindly. But there are situations when long term memorization is an essential part of the study process, for example if you’re trying to learn a new language. A common tool to help in this is flashcards, ie. cards each with a precise question on one side, its answer on the other.
When digging deeper on how to maximize the efficiency of flashcard review, the “when to review such or such card?” question naturally comes to mind. It turns out some people have been researching that very question and have come up with interesting tools and theories on how to best use your time when reviewing.
SuperMemo and spaced repetition
One such person is Piotr Wozniak, a rather eccentric Polish profressor who, since the early 1980s, has been studying and perfecting what he calls “spaced repetition“. His software, SuperMemo, implements this technique.
Essentially, once a flashcard is made and reviewed for the first time, it is then scheduled to be reviewed some time in the future, say in 2 days. Then, depending on how well you remember it in 2 days, it is rescheduled for a next review, but this time further in the future, say in a week. The process is then repeated, spacing repetitions further and further until a point where you won’t forget about it anymore.
The core idea behind spaced repetition in SuperMemo is to present the flashcard just when you’re about to forget about it. Dr Wozniak has developped and refined models of how memorization and forgetting happens in time. The end goal, of course, is to repeat a minimum number of times a given flashcard, so you can repeat more flashcards total.
The SuperMemo website details his findings and tips concerning memorization, and can make for hours of reading. In particular, there are techniques to make better flashcards (how to formulate the question, etc.) and to use the SuperMemo software, of course. There is also an affiliated site where you can find ready-made flashcard sets available for purchase.
EDIT: On the website, you can notably find more detailed information on the mathematical details of the algorithm used by the program and its evolution. As mentioned in a comment below by FlashcardDB creator, the Leitner system is another spaced repetition system which doesn’t rely on computers (it was created in the ’70s), but on moving real cards in real decks, as explained on the FlashcardDB site itself.
Alternative software
Altough it seems Piotr Wozniak has been a pioneer in creating spaced repetition software, other programs have recently appeared that follows a similar model.
If you want something cross-platform (I run Linux so that’s my case), you can go for Mnemosyne. It’s much simpler than SuperMemo (much less options, formatting in flashcards, etc.), but it’s open source and free.
There are also Web versions. SuperMemo itself has an online version. Very recently, websites SpicyElephant, Mind Picnic and Flashcard DB (mentioned above) have appeared that follow the spaced repetition model. Being online communities, they allow you to share flashcards and reuse those made by others.
Update January 2010: a very good reference for alternatives is this comprehensive database of flashcard software.
References
EDIT: Side note: my own experience or lack thereof
Unfortunately, I do not have a lot of personal experience with this. When I was in high school I had programmed something similar for myself (my formula was real simple and very inflexible). That’s why I found it amusing to discover spaced repetitions a few months ago.
But these days I don’t deal with much information that would apply well to spaced repetition (I study software engineering). Encoding the Q/As is too much effort for the gain. Learning through application works better right now.
I’m trying to come back to it with other learning trails, though, as the principle is just so cool 
