Spaced repetition (SR) is a method for organizing your learning calendar in the most optimized way possible. It has two functions:
- Knowledge learned this way should be remembered forever,
- Remembering forever should use up the minimum amount of time possible.
¶ How does it work?
In practice SR is performed by creating flashcards and assigning them a forgetting index within a computer software.
Flashcard is generic term for any association of knowledge. An example is the association between two words in different languages: “Hello” means “Bonjour” in French. The reciprocal association “Bonjour” -> “Hello” is another flashcard. They can be physical (paper cards) or virtual (like in SuperMemo).
The forgetting index is a number that represents the likelihood (e.g. 10%) you will forget a given piece of knowledge (e.g. “Hello” -> “Bonjour”) before the next date on the calendar when SR has scheduled a review for it. For example, if on the 1st of January you learned that “Hello” means “Bonjour” in French, you might only be able to recall that with 90% certainty until the 20th of January. Past that date, the likelihood of recalling it will keep decreasing. This is because forgetting is exponential in nature:
Forgetting is avoided by reviewing your knowledge. Reviewing is the process of refreshing knowledge to ensure that it is persisted in memory. For example, on the 20th of January, you might quiz yourself:
What is the French translation for ‘Hello’?.
If you recalled correctly, then your memory of that knowledge will be persisted for an even longer time than you previously had, for example until March 31th with a 90% recall rate.
¶ Comparison Matrix
|
|
Spaced repetition |
Traditional learning |
|
Support |
Computer software*. |
Any (usually pen & paper). |
|
Study plan |
Automatically scheduled by the algorithm. |
Manually, either by:
|
|
Scalability |
High: the software knows everything you want to remember. |
Low: you cannot list everything you've learned and remember to review it. It is a circular problem. |
|
Time spent learning |
Minimal: the algorithm computes the optimum interval between reviews. |
Suboptimal: reviews will be random or arbitrary (e.g., for an exam). |
|
Chance of remembering |
As high as desired, depending on the forgetting index. |
Low, you will forget as soon as you stop using your knowledge. |
|
Frequency of learning |
As frequent as desired**. |
Arbitrary or random. |
*: Piotr Wozniak executed spaced repetition on paper for years before writing the first computer version with SuperMemo, read his article.
**: Missing out a few days is not the end of the world, but it will require more work later on!