List Length Effect

What is the List Length Effect?

The list-length effect is a change in memory performance when the number of studied items changes. In free recall, longer lists commonly reduce the proportion recalled, even when the total number recalled increases.

Recall and recognition

• Effect on Memory Recall

  The distinction between number and proportion matters: recalling 8 of 20 words is more words but a smaller proportion than recalling 6 of 10. These are illustrative numbers.

• Effect on Memory Recognition

  List length can also affect recognition. Comparisons must control factors such as the delay before testing, because longer study lists can introduce other differences.

• Where an item appears

  Kahana’s 2020 review describes list-length effects that differ by serial position: early and middle items can be more affected than final items.

What list length tells us

The effect helps researchers study memory search and competition. It does not identify one ideal list size for lessons, product displays, or marketing messages.

Why explanations differ

A lower recall proportion does not by itself prove that a fixed amount of memory was divided equally among items. Diana and Reder’s contextual-competition study discusses controlled recognition findings and competing interpretations.

The part-list cueing effect describes how showing some studied items can hinder recall of the remaining items.