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- R-Metric (Recall Metric)
- spaced repetition algorithms based on their ability to predict recall before a grade is scored. In SuperMemo 18, R-Metric is used solely to compare Algorithm SM-15 (known from SuperMemo 16) and the new Algorithm SM-18. It is shown as percentage in Statistics and Toolkit : Statistics : Analysis : Use : Efficiency : R-Metric. R-Metric is a difference between the performance of the two algorithms:
LSRMis the least squares predicted recall measure for a given algorithm. R-Metric greater than zero shows superiority of Algorithm SM-18. R-Metric less than zero indicates underperformance of the new algorithm.
LSRMis a square root of the average of squared absolute differences in recall predictions:
Recallis 0 for failing grades and
Recallis 1 for passing grades.
PredictedRecallis a prediction issued by the algorithm before the repetition. In Algorithm SM-18, the prediction is a weighted average of the value taken from the Recall matrix, and R (retrievability) computed from S (stability) and the used interval. The weight used is based on prior repetition cases which inform of the significance of the Recall matrix prediction (the prediction becomes more meaningful with more prior repetition data)