This page is an overview for the learning technique of spaced repetition, an effective way to learn and indefinitely retain knowledge. This technique is typically performed by reviewing digital flashcards, although these cards can also be paper. Typically, these cards consist of a question/answer pair written by the user: the user regularly reviews the questions written on these cards and attempts to recall the answer, before flipping the card to reveal the correct answer. If the answer was recalled successfully, the user moves on to the next card and the review interval increases i.e. the user sees this card less frequently in the future. If incorrect, the card is shuffled back into the deck and the review interval decreases.
Because reviewing and recalling this information requires only marginally more time investment than reading something for the first (and only) time, this technique is extremely efficient for aiding the learning process. This being said, there are still many important principles behind writing effective cards, setting up deck parameters, and customising spaced repetition software. This page is a growing collection of useful resources to encourage and improve the use of such systems.
Fernando Borretti identifies two 'limiting factors' which may explain why spaced repetition is not used by more people, despite the clear benefits:
- Habit Formation: Habit formation is difficult, and the nature of the scheduling algorithm means that reviews pile up if not reviewed almost daily. This can be discouraging and can deter many new users.
- Card-Writing Skills: Writing effective flashcards is a difficult skill and it takes trial-and-error before you can write cards which actually assist in recall.
Content consumption (aside from that consumed purely for leisure) should be approached with the intention of writing cards to extent one's own understanding. Articles, videos, and other media can all be leveraged for this purpose and, in fact, this mindset of looking to quantify learnings makes you much more likely to take away useful information, even if you are unable to capture cards in the process.
Too many types of note-taking are wasted effort because they are not designed around a medium which encourages reviews. If you do take notes on topics you're reading up on, be sure to take the time to convert this information into flash cards, to ensure the information is processed and able to be recalled in the future.
Andy Matuschak identifies the following principles for prompt writing:
- Retrieval practice prompts should be focused.
- Retrieval practice prompts should be precise about what they’re asking for.
- Retrieval practice prompts should produce consistent answers, lighting the same bulbs each time you perform the task.
- Retrieval practice prompts should be effortful.
- Wikipedia, Varied practice: Organise your decks such that when you sit down and review them, you're answering questions across a range of domains (e.g. geography, history, mathematics) - this allows you to make more connections between cards and keeps reviews more interesting.
- Reviewing your cards is an excellent opporunity to flag and/or re-write imprecise or incorrect cards. Constantly be on the look-out to improve them to align with the principles outlines in the prompt writing section of this page.
- Delete or suspend any cards you are no longer interested in anymore.
Anki is one of the most popular spaced repetition software applications and is open-source, except for the iOS app. It is highly customisable and has the largest number of shared decks and add-ons.
- Anki (GitHub): For desktop computers (Open Source)
- AnkiDroid (GitHub): For Android phones (Open Source)
- AnkiMobile: For iOS devices ($24.99)
Mochi is a free, cross-platform app with an option to upgrade to a Pro plan for additional features. Features a minimalist design.
- Dr. Piotr Wozniak: Effective learning: Twenty rules of formulating knowledge
- Andy Matuschak: How to write good prompts: using spaced repetition to create understanding
- Soren Bjornstad: Rules for Designing Precise Anki Cards
- Michael Nielsen: Augmenting Long-Term Memory