the cedar ledge

Spaced Repetition Systems

Date: May 25 2020

Summary: What are Spaced Repetition Systems and what is available?

Keywords: ##zettel #spaced #repetition #system #spacing #effect ##learning #software #archive


Not Available

Table of Contents

    1. Software Implementations
  1. How To Cite
  2. References
  3. Discussion:

There are multiple algorithms available used for effectively implementing the spacing effect. The earliest algorithm comes from the original discoverer of the spacing effect, Hermann Ebbinghaus. The algorithm has been replicated and scrutinized examined multiple times. [1]–[3] Spaced repetition systems are based around proper implementations of such algorithms.

Before the advent of computers, it was very difficult to implement such a system. The best system to take advantage of this effect was the Leitner System which used paper note cards to assist with remembering information. However, this was still a somewhat fragile system and difficult to manage.

With computers, there have been several pieces of software made to automate and keep track of repetitions for a learner. A majority of these systems directly adapted the Leitner System from the analog to the digital world. Each software generally has proprietary algorithms that supposedly maximize the spacing effect but are directly inspired by the original work done by Ebbinghaus.

Whether analog or digital, key features of these systems are as follows:

  1. Uses an algorithm implementation of the spacing effect for a user.

  2. Each piece of information is spaced automatically per a user's perceived difficulty in either remembering or processing that piece of information on a repetition.

  3. Pieces of information are generally presented in a "flashcard" format and are stored in "decks".

Software Implementations

There are many pieces of software that utilize spaced repetition. Provided is a table listing some of the most popular ones:

AnkiOpen source flashcard based learning software.@AnkiPowerfulIntelligent
DuolingoPopular language learning platform.@LearnLanguageFree
MemriseFlashcard based language learning app.@zotero-1378
QuizletMulti-faceted learning platform.@Quizlet
SupermemoSoftware for spacing and incremental reading.@LearnFastForget

How To Cite

Zelko, Jacob. Spaced Repetition Systems. May 25 2020.


[1] J. M. J. Murre and J. Dros, “Replication and Analysis of Ebbinghaus’ Forgetting Curve,” PLoS ONE, vol. 10, no. 7, p. e0120644, Jul. 2015, doi: 10.1371/journal.pone.0120644.

[2] H. Ebbinghaus, “Ueber das gedächtnis,” 1885.

[3] E. L. Bjork, R. A. Bjork, et al., “Making things hard on yourself, but in a good way: Creating desirable difficulties to enhance learning,” Psychol. Real World Essays Illus. Fundam. Contrib. Soc., vol. 2, no. 59–68, 2011.


CC BY-SA 4.0 Jacob Zelko. Last modified: January 17, 2023. Website built with Franklin.jl and the Julia programming language.