Getting the most out of spacing involves figuring out the right amount of time to space. This is important because better recall is positively correlated with the amount of spacing up until a certain point, after which recall begins to worsen with longer spacing intervals. The optimal amount of spacing depends on the RI, with longer RIs corresponding to longer periods in between spacing. Demonstrating this is an example from a study by Cependa et al., who showed that "the optimal spacing gap for a one-week test delay is about one day, while the optimal spacing gap for a one year test delay is about three weeks"

Comparing spacing and retention intervals

The spacing interval refers to the interval of time separating different study sessions (aka: lag).

University of Michigan - Ann Arbor

The two main variables influencing the spacing effect are the spacing interval (lag) and the retention interval (test delay).

Spacing effect variables

Carvalho, P. F., Sana, F., & Yan, V. X. (2020). Self-regulated spacing in a massive open online course is related to better learning. *npj Science of Learning*, *5*(2), 1-7. https://doi.org/10.1038/s41539-020-0061-1

Self-regulated spacing in a massive open online course is related to better learning

The retention interval, or RI, refers to the amount of time following the last spaced study session before a final test (aka: test delay).

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