Spaced repetition

Why we forget#

Back in the nineteenth century Hermann Ebbinghaus, memorising nonsense syllables, noticed that most of what is learned is lost in the first days, after which forgetting slows down. This relationship is called the forgetting curve. The exact numbers depend on the person and the material, but the shape is always the same — a steep drop at first and a gentle tail afterwards.

The second observation matters more: every successful act of remembering slows down the next round of forgetting. Recall a word after a day and it lasts longer; recall it again a week later and it lasts longer still. The method is built on that.

How the schedule works#

The idea is to lengthen the gap after every successful review. A simple version you can keep in a calendar or a notes app:

• first review — the next day;
• second — three days later;
• third — after a week;
• fourth — after two or three weeks;
• after that — once every one or two months.

If you fail to remember, the material goes back to a short interval. Flashcard apps do the same thing automatically and adjust the intervals to how easy each answer is for you.

Reviewing means recalling#

The main mistake is rereading. Rereading gives a feeling of familiarity but does not train retrieval from memory. A proper review is a question without a hint: close your notes and answer, look at a word and say its translation, solve a problem without the worked example. A mistake here is useful — it shows what you need to review sooner. The technique is covered in detail in active recall.

What works on flashcards and what does not#

Flashcards are good for atomic facts: words, formulas, dates, definitions, commands. One card holds one question and one short answer. "What does git status do?" is a good card. "Tell me everything about git" is a bad one.

Skills are not memorised that way. Solving problems, playing an instrument and writing require repeating the action itself: go back to old exercises before new ones, and once a week solve a couple of problems from chapters you have already covered. The schedule stays the same — growing intervals.

How to fit it into your week#

Set aside the first ten to fifteen minutes of every session for review. Old material first, then new: that way review never gets postponed "until later". If you missed several days, do not try to catch up all at once — go through the oldest items and continue at your normal pace.

Keep a note of what you reviewed and when. After a month this log shows which topics stick and which you have to review again and again — the second kind is worth explaining to yourself from scratch rather than simply drilling.

Step-by-step plan

1. Break the material into questionsOne question, one short answer. For skills — a list of exercises.
2. First review the next dayRecall without hints and mark your mistakes.
3. Growing intervalsThree days, a week, two or three weeks, a month; after a mistake — back to a short interval.
4. Review at the start of a sessionTen to fifteen minutes on old material before the new.
5. A review logWhat you reviewed and when; topics that will not stick get re-explained from scratch.

Sources

• AnkiA free flashcard program with spaced repetition built in
  free
• Forgetting curve — WikipediaThe history of Ebbinghaus's observations
  free

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