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Spaced Repetition: Learn Once, Remember Forever

Do you remember all those nights before an exam with a huge textbook in your hands, knowing that you don’t remember at least half of the curriculum? The overnight hours of studying, until you just couldn’t read a word more? This very common process has proven to be effective for millions of students over the years. Its name is “cramming”. But as effective as it seems to be for performing okay in an exam, it’s plainly awful for long-term retention. For that, you need another way of studying, namely “spaced repetition”.

In the lates 1800s, Hermann Ebbinghaus performed a large series of memorization experiments on himself. He tried to memorize random syllables, and then he tested himself at different intervals to see how much he could recall. The result was Ebbinghaus’ Forgetting Curve, illustrated below, and the importance of his work has carried over until today.

Ebbinghaus Forgetting Curve

As you see in the image, it only takes a handful of minutes to lose an important amount of retention. It’s an even bigger problem when we start talking in days.

To solve this problem, the spaced repetition learning system was created.

What is Spaced Repetition?

The main idea behind it is actually quite simple. If you revisit knowledge long enough after you initially learn it, but before you need to relearn it completely, your retention will be boosted dramatically. In order to achieve long-term results, you need to review the knowledge in increasing intervals. In the illustration below you can see exactly how this works in order to prevent you from forgetting the knowledge.

Spaced Repetition Wired Graph

Spaced Repetition Graph. Notice the increasing intervals between reviews. Source:

The first part of the main idea stems from the necessity to avoid cramming. Regardless if it seems effective, repeatedly reading the same material continuously does not provide any long-term benefit. With very short intervals between revisions, your brain gets bored and disregards that information, as it does not put any effort into recalling it.

The second part, revisiting before having to relearn is also very important. If you let too much time pass between revisiting knowledge, it will be like starting from scratch; the forgetting curve will have been reset.

Moreover, learning does not always come from solitary reading. If a couple of people tell you their names, it might be insulting to have to ask them again after a while. Or if you want to retain the content of a speech, you probably won’t have the chance to witness it again. In such cases, it is very useful to promptly revisit the knowledge before forgetting it.

Does spaced repetition apply to everything?

When I first got introduced to the concept of spaced repetition, I was the biggest “crammer” I knew. I’d always leave studying for the last minute, and therefore my long-term retention was awful and my mental models weren’t getting any stronger. I was also performing quite well on exams that way, and thus I didn’t think I needed to change anything.

At the same time, though, I was trying to learn a new language, namely Spanish, and for the first time in my life, I was trying to self-educate, rather than get a teacher. I soon discovered that cramming was useless with no exam schedule, and so I had to figure out another way to learn. Eventually, I started using the language learning app Duolingo, which utilizes a spaced repetition system.

The results were profound, and for the most part, I’ve switched over from cramming. Since then, I’ve used spaced repetition to learn a language, how to play the guitar, how to memorize a deck of cards and much more.

This led me to understand that spaced repetition can be utilized in a myriad of subjects. It is a system that works because of the way our brains function, regardless of the particular subject. Although the specifics vary for each individual, the forgetting curve applies to everyone. For that reason, you should, after grasping the basic concepts, move on to restructuring all your learning to utilize spaced repetition.

Where does spaced repetition NOT apply?

It stands to reason that there are some occasions where spaced repetition won’t be as helpful. If the skill you are trying to develop is very complex or strictly mechanical, spaced repetition won’t provide many benefits to your process.

In case of mechanical skills, like sports, more consistent practice is necessary, in order to develop the necessary muscle memory. You still have to space out the practice and not cram it in a single day, but you also shouldn’t keep increasing the intervals like in knowledge-based practice.

In very complex skills like advanced math, though, spaced repetition can be applied, but you first have to effectively deconstruct the skill to smaller and specific chunks, which you will then move on to learn and memorize through spaced repetition systems.

How to use spaced repetition in your life

Probably the most important question by now is how you can determine the exact point when you should revisit the knowledge in question. Well, you can’t. At least not perfectly. The most effective way is to rely on software, where you don’t have to worry about the underlying algorithm. The one I use is called Anki.

Anki expands on the concepts of flashcards by adding a measure for when you should again review the material. That measure is how “hard” it was for you to recall each card. It then uses its spaced repetition algorithm to present you each flashcard at the correct moment, thus maximizing your retention.

(Anki is available both on the web and on mobile. This way you can use it on all those “wasted” moments, like waiting for the bus, in the subway or when waiting in the queue for your coffee.)

Can I use spaced repetition without software?

In case you don’t want to use Anki or any other software, you could always develop your own spaced repetition flashcards system using the “Leitner system“. It is a simple implementation of the principle, which uses the concept of boxes that have designated timeframes for reviewing. For instance, the first box is reviewed daily, the second box every 3 days, etc. Each card, when answered correctly, gets moved to the next box, and in case you can’t recall it, the card should be returned to the first box. This way you get a good approximation of the Anki system.

Leitner Spaced Repetition System

Is spaced repetition enough on its own?

The answer is, in short, no. Spaced repetition is a great way to retain information in the long-term, but you still have to utilize the correct techniques to initially learn and correctly connect the new knowledge with pre-existing one. See my previous article on deliberate practice to find out how to learn and practice new knowledge, and see my article on the 80/20 rule to find out how to choose what to study. Combined with spaced repetition, you will be surprised by the speed at which you will be picking up new skills.

So, should I stop cramming?

Once again the answer is no. Cramming can be very effective in particular scenarios like performing well in an exam. Also, if there are only a couple days/hours left until your exam, you don’t really have much of a choice.

To be honest, I still cram whenever necessary. But spaced repetition is the prominent method for long-term retention, and you should utilize it wherever possible. If you still got the whole semester ahead of you, it’s time to start.

Call to Action

As you start utilizing spaced repetition in your life, you will witness various new achievements and/or struggles. I’d love to hear about them. Post on the Facebook group, or contact me directly!

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