Partial correlation

The partial correlation shows the relationship between two numbers after the linear influence of one or more further numbers has been removed from both. The question is how strong the relationship is at the same level of the further numbers.

Example: Shoe size and reading test are strongly related in primary school children (r = .54). With age removed, hardly anything is left (pr = .08).

Caution: Only what was measured and chosen is removed. The partial correlation does not show cause and effect.