Spaced Repetition Increases Memory Retention

Dr. Jill Alban, Ed.D., is Director of Academic Support at Touro University California.

We have all heard that learning medicine is like drinking from a fire hose.  


Hmmmn, refreshing!

Yet often the most effective study techniques available are not implemented. Spaced repetition is a powerful, evidence based study technique that can enhance learning and long time retention of medical knowledge. Graduate students in a variety of disciplines, but most especially medical students, could benefit from understanding and using spaced repetition to produce more knowledgeable and better-informed doctors.

Over a hundred years ago, a German psychologist, Hermann Ebbinghause, used careful experiments to determine how learning and forgetting works.  From these experiments, he described a “forgetting curve” in which “large amounts of forgetting occur quickly, followed by a more slow and steady decline in retention. Forgetting happens almost immediately after a student learns something. Within 20 minutes of learning some new information, students can only recall about 60 percent of the information they just learned. By 9 hours, retention is less than 40 percent, and by 10 days, a mere 20 percent.

hermann-ebbinghaus sketch.jpg

Hermann Ebbinghaus found that being exposed to information at a series of successively longer intervals increased memory retention.

These results led to another key observation by Ebbinghause, “Learning events that are repeated over time result in more efficient learning and greater retention compared to exposure to a single review of material.” Learning events that are repeated over time is a psychological finding termed the “spacing effect.”

A recent article remarked that, “The spacing effect is arguably the most replicable and robust finding from experimental psychology. Hundreds of articles, including a number of reviews and meta analysis have found a spacing effect in a wide variety of memory tasks.” Spaced repetition, a technique in which students review material according to a schedule determined by the spacing effect, has been found to be effective in numerous educational contexts.

It shouldn’t be surprising, then, that some researchers have investigated the spacing effect in medical education. In one randomized controlled trial of the spacing effect, Kerfoot et al, found that spaced learning improved the retention of clinical knowledge by medical students at Harvard. After a one-week urology rotation, the students were split into two groups. Each received a series of spaced review emails. One group got questions on one-half of the topics in urology and the other group got questions on the other.


This chart, from, illustrates how spaced repetition helps build long-term memory.

At the end of the year, each student group did significantly better on the topics that they received questions about. This study did not attempt to compare spaced repetition with more typical study techniques, but it did show that a relatively small time investment into spaced studying could lead to significantly improved retention.  At the resident level, where retention of knowledge is arguably even more important, the spacing effect has been shown to work as well.

And spaced repetition does not require the instructor driven methods used in these studies. Many of you, on your own initiative, now use free, flashcard apps, such as Anki and Mnemosyne (nemosini)  in your studies. Ideally the program should prompt you to review a fact as soon as you are in immediate danger of forgetting it. Students have been able to use these tools for all aspects of medical learning, from biochemistry to clinical guidelines. Many of you are already pooling your learning efforts by collaborating and creating shared flashcard decks.

The catch, however, is that the spacing effect requires patience and diligence. And many of you have gotten quite far in your academic careers by doing exactly the opposite, through cramming. Why is that? Well, the simple truth is that massed learning, more commonly known as cramming, does work in the short term. You can load up your memory with information, and some of it will stay there for a time.

Yet as anyone who has ever crammed for a test can confirm, the gains are merely temporary, in keeping with Ebbinghaus’ confirmed findings. All those efforts yield little long-term knowledge! 

In fact, by the time you arrived at medical school, most of you have forgotten the majority of what you learned in your college courses. How many of you have discovered that you need to re-learn massive amounts of forgotten information from your undergraduate years? Students routinely need to re-learn massive amounts of forgotten information before taking their board exams, and residents eventually forget much of what they learned in medical school outside their specialty. All of this translates into vast amounts of time wasted.

Students routinely need to re-learn massive amounts of forgotten information before taking their board exams, and residents eventually forget much of what they learned in medical school outside their specialty. All of this translates into vast amounts of time wasted.

Fortunately, spaced repetition is a strategy that all students can employ to enhance medical education and all other professional disciplines as well. Many of you are already investing time in electronic flashcard programs to enhance your retention for block exams, board exams and beyond. As more students understand the tradeoffs between spaced studying and cramming, they can make more informed decisions about how they want to navigate learning in professional school.

Touro provides an opportunity to use spaced repetition. By having block exams rather than weekly quizzes, those of you who choose to focus on long-term retention rather than cramming are not penalized.

The power of modern medicine is in large part the result of an explosion of our understanding of the human body. As a result, medical education  grapple with how to teach students and residents ever-increasing amounts of information to train you as clinicians. By harnessing the power of spaced repetition, students and medical schools alike can work to learn more effectively and create better-informed doctors.   


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