# Recall

**Memory recall** is the ability to bring things back from memory. When expressed as percentage, it can also be called **retention**. It is one of the measures of retrievability (R) for a population of memories. For example, if we remember 8 items from a list of 10 memorized items, we speak of the recall/retention of 80% (R=0.8). In a population of memories with retrievability R, average recall is R independent of memory stability.

A forgetting curve shows the drop in average **recall** in time. Immediately after learning or review, the **recall** may approach 100%. The speed at which recall drops over time depends on memory stability.

This glossary entry is used to explain "*I would never send my kids to school*" (2017-2024) by Piotr Wozniak

Figure:The first forgetting curve for newly learned knowledge collected with SuperMemo. Power approximation is used in this case due to the heterogeneity of the learning material freshly introduced in the learning process. Lack of separation by memory complexity results in superposition of exponential forgetting with different decay constants. On a semi-log graph, the power regression curve is logarithmic (in yellow), and appearing almost straight. The curve shows that in the presented case recall drops merely to 58% in four years, which can be explained by a high reuse of memorized knowledge in real life. The first optimum interval for review at retrievability of 90% is 3.96 days. The forgetting curve can be described with the formula R=0.9906*power(interval,-0.07), where 0.9906 is the recall after one day, while -0.07 is the decay constant. In this is case, the formula yields 90% recall after 4 days. 80,399 repetition cases were used to plot the presented graph. Steeper drop in recall will occur if the material contains a higher proportion of difficult knowledge (esp. poorly formulated knowledge), or in new students with lesser mnemonic skills. Curve irregularity at intervals 15-20 comes from a smaller sample of repetitions (later interval categories on a log scale encompass a wider range of intervals)