What is Spaced Repetition

tl;dr: The SR algorithm is to calculate when it's time someone should relearn something, so he or she can keep it as knowledge with the least effort and the least amount of time. Exploiting it by individuals is made possible with the advent of software.

No matter the profession or field of study – in today’s world memorizing a plethora of information has become virtually mandatory. This goes especially for studying a particular data-driven field, such as medicine or law – anything that requires lots of knowledge, really.
Accumulating an abundance of data in order to complete any given task has long been one of the most frustrating challenges academia presents us with. For example, medical students are expected to know each and every bone and muscle in the body by name. When attempting to learn a new language, the amount of vocabulary that needs to be memorized is insurmountable. I could go on, but I’m sure at this point you’ve understood the concept, so feel free to insert any case study you find most relatable. And even if the necessary knowledge has been internalized, at some point you are bound to forget it – and the cycle begins anew.
This is not news for psychologists: It has long been known that the ineptitude of many to achieve greatness in particular fields is not grounded in too complicated topics or IQs that simply do not score high enough. Learning is the easy part, remembering is where it gets tricky. That’s because our brains are built to function best when fed with information constantly over a longer period of time. When we learn something new, the information has (assuming it even makes it to long-term memory) a certain half-life; meaning an amount of time after which it is forgotten.
And this is where Spaced Repetition comes in.
Basically, what SR means is this: constantly reviewing simple bits of information over a long period of time. The repetition is stretched out over days and weeks and through this process the data is slowly burned into our memory. Cognitive psychologists are very aware of this effect and have been telling us about this since at least the 50s. Seeing as Spaced Repetition is yet to be put to use on a broad scale, it just might be the most snubbed memory-hack in the history of learning.
If you’ve never heard of Spaced Repetition before, you might take this for some voodoo nonsense - something along the lines of potency vitamins even. However, this couldn’t be further from the truth. The spacing effect has been known since the 1800s and has been explained in numerous scientific papers over the years (look no further than Philips et al, 2013). With all this iron-clad research being done and delivering conclusive evidence in favor of employing this method, the question arises: Why exactly aren’t people the world over using it?
Spaced Repetition exploits the above-mentioned function of the brain to store memories better if they’re reviewed over longer stretches of time. For example, if there is a particular piece of information you need to remember the solution in accordance with Spaced Repetition is to learn it one day, then review it again two days after that and then again two days after that. That way, the information is committed to long-term memory and will always be at your disposal, should you need it. The reason for this is also mentioned in the scientific findings. Think again of the radioactive half-life analogy; right after the bomb strikes, radioactivity will be at its highest. It will then continuously decrease by fifty percent. So, if you are an evil genius of sorts and want to make sure a certain area is radioactive for the longest possible timespan, you would need to nuke the place again once the level of radioactivity has significantly decreased and is about to be unnoticeable. That will get you furthest while keeping radioactivity levels high as opposed to dropping all your nukes tail-to-tail or even all at once. Now, away from nuclear bombing and back to memorizing. The same principle applies here: if you want to remember something for a very long time, you need to feed your brain the information again at a point when it has almost forgotten the data in question. However, determining the exact moment when another learning session is required to hang onto the knowledge in question eludes the human brain. This is where the SR algorithm comes in, allowing to remember data for as long as possible with the least amount of effort.
Another point of interest will presumably be the actual workload required. How much learning will have to be done on a daily basis to ensure the positive effects of Spaced Repetition? As you might have guessed at this point, this has also been studied. Experiments with test groups showed that rehearsing about 90 – 100 pieces of information formulated as questions (which amounts to about 20 minutes of practice per day) were sufficient to create a significant spike in performance over time. With two about equally capable test subjects, the one using Spaced Repetition was able to outperform the other (not subscribing to any specific form of studying) by a whopping fifty percent.
If you are in a place in your life where you find yourself studying often but getting nowhere academically, advancing only your levels of stress and frustration, Spaced Repetition is for you. If you want to improve yourself by vastly increasing your knowledge – the SR-algorithm will greatly advance your ambitions. So, you can hack your brain and take your memory to the next level using the Spaced Repetition algorithm.