Spaced Repetition: Overview

**Spaced Repetition** is _reviewing_ each fact _just often enough_ so that you don't forget it.

If you don’t have a review program, you will forget almost everything you learn. For most of human history, people have used various ways to cycle through and renew their knowledge. Think of seasonal festivals or liturgical prayer. Spaced repetition is an exciting new way to review that may be the most efficient method yet.

Normally, when you use a deck of flashcards, you have no idea how often you should look at each card again. Either you don’t keep up with reviews, and forget everything all over again, or else you review the whole deck over and over again. And that gets old fast.

With spaced repetition, you review each fact just often enough so that you don’t forget it.

Why spaced repetition matters

Spaced repetition is long-term review. This is the exact opposite of the typical approach: one-time or infrequent tests and exams.

Quizzes and tests don’t really work.

A single quiz, test, or exam is only a snapshot. Your grade reflects only what you know on that date.

Imagine a summa cum laude senior retaking freshman finals. She would probably fail.

Real memory is ongoing, through your whole life

This is totally different from the “cram-for-the-test” ethic.

You must keep renewing your knowledge. Your brain changes. It’s alive, growing. If you don’t review, you lose what you’ve learned.

Your brain naturally forgets.

Your brain naturally forgets, and usually, this is good. Do you really want to remember the colors of everyone’s socks? Forever?

When you first learn a thing, you have a short time to convince your brain that, unlike sock color, this is important.

It can be as little as one hour. Otherwise, your brain tosses it.

But if you review at the right times, your brain will remember.

Every time you review, you can wait about twice as long before your next review.

This means a bunch of repetitions right at the beginning, and then far fewer later on.

A conservative spaced repetition schedule

There is no perfect schedule for spaced repetition. Researchers are still trying to fine-tune the algorithm. Personally, I doubt the same algorithm would work for all people or all material anyway.

But here is a basic schedule. These seem to be the intervals that will usually work.

First, repeat the fact a few times, until you feel like you remember it. For short facts, that’s enough, and you can wait for your next review.

For clusters of verses, or other complex material, you may want to repeat the material two or three times a day, over the next three days. This allows you to relax and take your time to make your initial memorization.

Once you feel like you know it, wait 4 days. Then review. Sometimes the fact will still be easy. Other times, remembering will be a lot harder than you thought. That’s the magic of spaced repetition. Four days ago, you felt like you’d remember this forever. But when you check up on it, you find out you need to review.

After that review, you can wait one week. The chart shows the rest of the intervals.

ReviewInterval
A1st day, 3–4x/day
B2nd day, 2–3x/day (only for texts, or other complex material)
C3rd day, 2–3x/day (only for texts, or other complex material)
D4th day, 2–3x/day (only for texts, or other complex material)
E4 days after you stopped reviewing
F1 week
G12 days
H3 weeks
I1 month
J2 months
K3 months
L5 months
M9 months
N6 months
O2 years
P6 years
Q11 years
R18 years

And so on. Many reviews at first. But once you get past that hurdle, you have far fewer reviews.

Again, notice how ordinary study habits are the exact opposite. In school, you learn something, then don’t see it again till the test, then wait even longer before the exam. With all that space between reviews, you have to relearn most of the material every time.

If you miss the answer, you basically go back and start over again. However, a computer program may look over your whole history with that card, and decide you can move back up the chain a little faster this time.

This is a conservative (repetitious) schedule. The flashcard program Anki uses even fewer repetitions.

You can use either computer flashcards or paper flashcards. Computer flashcards are a lot less work, as long as you’re already used to maintaining a computer — and backing up your data! Otherwise, you might prefer paper flashcards.

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