# Spacing effect

**Spacing effect** is a greater memory increase in successful recall that comes later in time.

**Spacing effect**can be expressed precisely with the help of the

**stabilization curve**, which defines the effect as

*Gain*in memory stabilization over time. For details see: Stabilization curve

**Spacing effect** has positive and negative interpretations leading to a degree of confusion:

**positive interpretation**for long intervals (aka stabilization): if we increase intervals in learning (to a degree), we can improve learning (i.e. spacing effect is helpful)**negative interpretation**for short intervals: if we review too often, the results of the review will be ignored by the memory system (i.e. spacing effect is harmful)

In the two component model of memory, we use a stabilization function, which resolves the above confusion by stating that each individual memory trace has an optimum review time that maximizes the expected memory effect, which is a resultant of the stabilization, and the probability of forgetting.

SuperMemo makes it possible to maximize the memory stabilization.

Data derived from the approximation of the stabilization curve in SuperMemo indicate that *gain* drops significantly with stability and increases slightly with difficulty. In other words, the old Bjork maxim stands: *the harder, the better*.

For those who care little about long-term retention of knowledge, SuperMemo may also be considered a tool for the improved brain power.

See also:

This glossary entry is used to explain SuperMemo, a pioneer of spaced repetition software since 1987

Figure:Stabilization curvecomputed with SuperMemo. The horizonal line shows time expressed as memory retrievability. The vertical line shows stabilization, i.e. the increase in the durability of memory expressed as an increase in memory stability. Blue circles show how much stability increases with review that takes place at a given level of retrievability. The size of the blue circles depends on the number of data points collected. The graph has been produced using 31,721 repetitions in SuperMemo in data quantiles of difficulty=0.53 and stability=26 [days]. Stabilization increases from 1.36 at retrievability=100% (SIncMin=1.36) to 26.31 at R=0% (SIncMax=26.31). Optimum review at R=90% in SuperMemo produces stabilization of 1.86 (Stab90 is an equivalent of O-Factor in older SuperMemos). The Gain constant that expresses the spacing effect equals 2.96, i.e. relatively high as befits a low stability quantile. Stabilization in this dataset can be computed accurately with the formula (yellow line): 26*e^{-2.96*R}, which produces a tiny deviation of 0.5069. The consolidation curve is shown in purple, and indicates that the forgetting index is a plausible learning criterion for the presented dataset. For R approaching 100%, the actual stabilization for the presented graph is 0.879 as obtained with 2074 measurements. This is not clearly visible in the picture, but can be investigated with stabilization matrix exports in SuperMemo. This means that the stabilization curve formula may be inaccurate at the extremes of retrievability approaching 100% and 0%. This can be explained by the fact that no memory is perfectly retrievable or verifiably obliterated (see: We never forget)