Absolute Versus Relative Forgetting

Slamecka and McElree (1983) and Rivera-Lares et al. (2022), like others before them, factorially manipulated the number of learning trials and the retention interval. The results revealed two unsurprising main effects: (a) the more study trials, the higher the initial degree of learning, and (b) the longer the retention interval, the more items were forgotten. However, across many experiments, the interaction was not significant, a finding that is often interpreted to mean that the degree of learning is independent of the absolute rate of forgetting (i.e., the absolute number of items forgotten per unit time). Yet there is considerable tension between that interpretation and the fact that forgetting has long been characterized by a power law, according to which the absolute rate of forgetting is not a particularly meaningful measure. When the power function is fit to the same data, the results show that a higher degree of learning results in a lower relative (i.e., proportional) rate of forgetting. This raises an interesting question: which of the two definitions of "forgetting rate - (absolute vs. relative) is theoretically relevant? Here, I make the case that it is the relative rate of forgetting. Theoretically, the explanation of why a higher degree of learning is associated with a lower relative rate of forgetting may be related to why, as observed by Jost (1897) long ago, the passage of time itself is associated with a lower relative rate of forgetting.