General information about spaced-repetition learning

Spaced-repetition is a methodology that has proven successful in the learning of facts, concepts and vocabulary items.

• The repetition consists of the repeated requirement to prove or attest that one remembers that particular fact, concept or word. In cognitive terms this means that the fact, concept or word has entered the long-term memory.
• The spacing refers to the intervals at which the fact, concept or word is presented to the learner with the requirement to prove or attest that they remember it.

If a learner reviews a list of twenty vocabulary items every day, then we have a simplistic spaced-repetition interval, i.e., daily. But the benefits of the spaced-repetition methodology are best attained by setting the review interval in a more sophisticated way.

This more sophisticated and effective methodology goes something like this:

• The learner is presented with a prompt (for example, a question or a word to translate).
• If the learner fails to remember the answer or translation, then she is presented with the prompt again within a short amount of time; for example: ten minutes or one day.
• If, on the other hand, the item is remembered, then the interval at which it is presented again for review is set to a date further into the future; for example: three days or one week. This interval is increased each time the learner proves or attests remembrance of the item.

  A typical day-based spaced-repetition interval sequence for successfully remembered items is: 1 - 3 - 8 - 21 - 54 - 137. In this example the spacing doubles by approximately 2.5 for each successive interval.

Before the internet, spaced repetition learning used flashcards, for example the very influential Leitner methodology. While these physical cards are still popular with some people, they have largely been replaced by computer apps. Computerised spaced learning uses the power of algorithms to offer more sophisticated and customisable spacing methodologies.

Probably the most popular of the current spaced-repetition apps is Anki. It is a highly customisable program with quite a steep learning curve. A Google search on spaced-repetition will present you with a huge number of articles and videos on the benefits of Anki and how to use it.

Here is a good short video (13 minutes) that explains very briefly the process by which new information or learning enters the long-term memory. It also has a clear explanation of the algorithm underpinning Anki's spaced-repetition intervals.

Note: Anki has changed its algorithm over time as ongoing research provides insights into the optimal intervals. Other spaced-repetition (remove italics) apps use different algorithms.

Here you can read about the methodology used in the spaced-repetition app on this site.

Wikipedia has more about spacing algorithms on its spaced-repetition page. The article includes a brief comparison of the efficacy of uniform intervals (e.g. every 5 days) versus expanding intervals (e.g. 1-5-12-23).