Spaced Repetition Research: What Science Says
Spaced repetition isn't just a "hack". It's one of the most replicated findings in the history of psychology. Here is the evidence.
1. The Ebbinghaus Forgetting Curve (1885)
Memory: A Contribution to Experimental Psychology
Summary: Hermann Ebbinghaus was the first to rigorously study memory. He memorized thousands of nonsense syllables and tested his recall at various intervals.
Key Finding: Memory loss is exponential. We lose ~50% of new information within an hour and ~70% within 24 hours unless reviewed.
Relevance: This established the biological necessity of review.
2. The Spacing Effect (Melton, 1970)
The Situation with Respect to the Spacing of Repetitions
Summary: Melton reviewed decades of research and confirmed that "massed practice" (cramming) leads to poorer long-term retention compared to "distributed practice" (spacing).
Key Finding: Spacing out reviews over time makes the memory trace more resistant to decay.
3. The Testing Effect (Roediger & Karpicke, 2006)
Test-Enhanced Learning: Taking Memory Tests Improves Long-Term Retention
Summary: Students were divided into two groups: one re-read a passage 4 times, the other read it once and was tested 3 times.
Key Finding: The testing group significantly outperformed the re-reading group on a final exam one week later. This proved that Active Recall is superior to passive review.
Relevance: Flashcards (which force a test) are biologically superior to highlighting or re-reading notes.
Modern Application
Today, algorithms ranging from SuperMemo's SM-2 to the modern FSRS use these data points to predict the precise moment of forgetting. SpaceRep builds on this century of research to give you the most efficient study schedule possible.