The Case for Spaced Repetition

9 min readApr 13, 2019

I’ve previously talked high-level about how I started using spaced repetition and using Anki with Programming. The hard benefits of using Spaced Repetition in learning are documented in many places.

However, many popular articles supporting learning with Spaced Repetition only focus on learning languages. Why Spaced Repetition works and how to use it to learn well any learning materials are not always clear.

The simple explanation of why spaced repetition works is that people retain information much better when they study right before they forget. When we do review a piece of knowledge right before be forget, that piece takes us a longer time to forget in the future on an ever-increasing interval. In the modern day world, there are ways to use software to plan out that study right before your bran forgets that piece of information.

The way this mechanism works involves a bit of brain science. Let’s first use a story to illustrate the concept.

The Leaky Bucket Story

Imagine a bucket. It’s a fairly normal looking bucket used to carry water to and from a house.

The bucket has seen a bit of wear and tear from being used to hold water. It’s not a new bucket by any means.

Now let’s say a child comes along and sees the bucket. This child might have blonde hair, blue eyes, and look a like a mischevious version of Dolph Lundgren from Rocky 4.

The child sees the bucket and gets an idea. He runs home, grabs his dad’s power drill and decides to drill a bunch of holes in the bucket. Remembering something else he wants to do, the kid runs away with a smile on his face.

Later, the owner of the bucket, a professional-looking woman in her early 30s, grabs the bucket after a long day at work and carries it to the well.

Not having seen the holes in the bucket, she draws water from the well. After doing this a couple of times, she feels a cold wetness in her socks. She looks down and discovers the bucket is leaking water.

The well is close to the woman’s house. She is able to power-walk a couple times back and forth to her house and gather enough water to fill up her pot on the stove to make delicious stew for dinner. Mission accomplished!

The bucket represents our memories. Each day we fill our brains up with the water of our experiences and information we learned. Depending on the memory, after an interval of time, that drop of water leaves through a hole in the bucket.

Each day, we dump new water into the top of the bucket and the process repeats itself. Luckily, when talking about the brain, the water in the bucket also has a type of sediment inside. As water leaves from individual holes in the bucket, the individual drops leave behind a trace. When you happen to fill the bucket with the same drop multiple times, the hole it leaves from gains a filament that leaks less water.

Over time, the stickiness becomes solid. The solid holes can take months or even years for specific drops of water to leak out.

The place where the analogy breaks is here: unlike a regular leaky bucket, our brains optimize out information at a steady, fairly random rate. It happens outside of our conscious control. You can’t consciously predict when you will forget a specific piece of information, and the only practice that adds sediment to specific memories is to review them. This is the reason why we sometimes find it easy to remember actress’ names but forget the birthdays of some of our best friends we haven’t seen in awhile.

Every memory you have is subject to forgetting. Some memories feel stable because they have been repeated often enough and have become so “sticky” that it would take them past your expected lifetime to forget.

Why Use Spaced Repetition?

In traditional learning, it has been estimated that we forget about 90% of what we learn in school within a month after taking a class. [1] Due to high volume, lack of repetition, and a varying degree of interest, the amount of knowledge we learn in 12 years of compulsory schooling pales in comparison with what is required to perform at higher levels in technical fields in the working world.

Traditionally, the gap in knowledge between what we need for our careers and what we get from school is filled in naturally while we work. Even with the most nascent forms of spaced repetition, we can more than double the rate of what we remember from a particular source. With computer-based methods, we can retain up to 95% of what we learn.

Knowledge has also proved to be beneficial as the more knowledge we obtain, the better decisions we can make that creates a net increase in the good we bring to the world. [2]

As the requirements for creative knowledge continue to increase [3], the need for more efficient ways of learning and remembering well-formulated knowledge increases.

Following this train of thought, it’s easy to see that more well-learned knowledge equals higher creative potential[4], and higher creative potential equals higher performance. More creative potential results in better solutions to the world’s problems and can improve the lives of everyone on the planet. This fact has motivated one man to devote his life to optimizing the acquisition of knowledge we can obtain in our lifetime.

Making Water Stickier

Let me tell you another story. The story of a Polish man named Piotr obsessed with finding a better way to learn.

Piotr has researched human memory for decades. What started out as an experiment to facilitate his own learning in college turned into his lifelong work. Through his research he found a way to pinpoint the exact day we should study a piece of information to increase its stability in our brain. He and his friends in college decided to turn this idea into a business and use it to change learning throughout the world.

When we study at the correct time, the drop of water in our bucket is replenished with the most sediment, and we forget that piece of information more slowly in the future. Repeat this process enough times, and the time it takes to forget that piece of information spans longer than our potential lifespan.

The one bottleneck to this learning method is categorizing, scoring, and recording an ever-increasing amount of water we want to keep in our bucket. Luckily, Piotr’s interest in more efficient learning coincided with the initial rise in popularity of personal computers. Using computers, keeping track of which knowledge to review at what time became much easier.

Piotr wrote the first versions of the software to organize the information for him and plan his reviews. This software was released to the public, and the idea of a convenient, computer-based spaced repetition system was born.

Get Started with Spaced Repetition

The ease of which you start spaced repetition is related to how well you know what you want to learn.

The best situation for achieving success with Spaced Repetition is one where the goals are fairly clear. Even if learning itself is the goal, figuring out what you are passionate about will jump start your learning adventure.

My journey began with learning Chinese. At the time, learning Chinese well was the sole focus of my life. I was already watching television and listening to Chinese radio every day. I would write down new words that I learned, but I found myself in an endless cycle of forgetting and relearning a large subset of what I knew.

Realizing the inefficiencies of retaining the volume of words I needed in order to improve my Chinese, the concept of using SRS clicked in my head when I read about it and I started immediately.

Others have begun by using SRS for programming [5]. If you find something you really want to learn, you can begin to read articles about the topic and formulate material to learn for life.

Dive in, make some cards, and start your reviews. If you stick to it, you will begin to see the benefits SRS has in your life in a few months. Keep the course for longer periods of time and you will begin to feel your learning level up to a place you didn’t realize was possible.

You can learn anything you want to any proficiency level and retain it for life. This is equivalent to a super power. Choose wisely what you wish to keep in your brain forever.

Which Spaced Repetition System to Use?

The first step in learning to study with Spaced Repetition is choosing a program. A lot of people get stuck on this step and there are a few posts online talking to this point. [6] The program of choice doesn’t matter as much as creating a habit does.

Two of the most popular programs you can choose to use are Anki [7] and Supermemo [8]. If you want to use Windows and don’t mind paying 20+ dollars to purchase the software and support further research, I recommend you use Supermemo. If you want a free desktop version, cross-platform syncing and mobile support, I recommend you use Anki.

The actual software you use is less important than what content you choose to put inside. The frequency and way you use Spaced Repetition matter much more than the algorithm.

The Hardest Part of Learning with Spaced Repetition

When studying, it is important for you to study everyday.

The length of your study session doesn’t matter. The amount of cards you create and review doesn’t matter. The mood you are in somewhat influences how well you learn that day, but even that isn’t a large factor in your learning.

In order for you to maximize the benefit you receive from using Spaced Repetition, you must do your reviews every day. When you skip days (or multiple days), you are missing out on the optimal time for you to review some subset of the knowledge contained in your collection.

Miss a day here and there and you will still reap the knowledge consolidation benefits. Skipping multiple days in a row will eat away at the integrity of the memory of the knowledge contained in your deck.

This one rule is what I have found to be the hardest to follow. I have introduced spaced repetition-based learning to almost at thousand people. I have not met many who can set aside time each day to study. But I know you can do it!

Setting aside time each day to learn is so difficult I recommend you start out slow. If you add 30 new cards a day into your deck, by the time you finish one week you will already have 210 cards. Since your brain will naturally miss 3–10% of the time (depending on how you formulate your cards and which SRS program you use), you will need to review a large subset of your total learning material each day. These reviews stack up fast, and it’s better to create a fun habit of review that is manageable in the long run.

Add enough cards each day, and the time required to spend reviewing cards will sharply increase.

When you start any learning adventure, your habit is equivalent to an ice cube. First, focus on melting that ice cube into water. After you already have cold water, heat that water up to be warm. Later, after you have already let yourself feel the success of making warm water, focus on rising that water to a boil and feel the heat from your success.

Change is hard in this world. It takes time to change your life and grow into the person you want to be. It is much faster to boil water when you start from warm water rather than try to start from ice.

When beginning SRS, start 10 minutes a day. Better yet, start 5 minutes a day. If you can commit to 5 minutes a day, after 2–3 weeks, 5 minutes will feel easy. You will almost feel obligated to move to 10 minutes because 5 minutes will feel like a joke.

Wash, rinse, and repeat. Eventually, SRS will become a staple of your day, and you will find you learn much more than you ever thought possible.

Sources:

5. https://www.jackkinsella.ie/articles/janki-method

6. https://www.reddit.com/r/Anki/comments/67icgg/anki_or_supermemo/

7. https://apps.ankiweb.net/

8. https://www.supermemo.com/