What, exactly, do number line estimation tasks measure? Different versions of the task were observed to have different effects on performance.

We investigated associations between the production (indicating the location) and perception version (indicating the number) of the bounded and unbounded number line estimation (NLE) task and their relationship to arithmetic.

A stronger correlation was observed between the production and perception version of the unbounded than the bounded NLE task, indicating that both versions of the unbounded—but not the bounded—NLE task measure the same construct. Moreover, overall low but significant associations between NLE performance and arithmetic were only observed for the production version of the bounded NLE task.

These results substantiate that the production version of bounded NLE seems to rely on proportion judgment strategies, whereas both unbounded versions and the perception version of the bounded task may rely more on magnitude estimation.