A partial correlation is a measure of the relationship that exists between two variables after the variability in each that is predictable on the basis of a third variable has been removed. A partial correlation, like a conventional Pearson product-moment correlation, can range from −1 to +1, butitcan be larger or smaller than the regular correlation between the two variables. In fact, a partial correlation is simply a conventional correlation between two sets of scores. However, the scores involved are not the scores on the original variables but instead are residuals-that is, scores reflecting the portion of the variability in the original variables that could not be predicted by a third variable.

As a concrete example, a researcher might be interested in whether depression predisposes individuals ...