Semi-Partial (or Part) Correlation

The semi-partial or part correlation is similar to the partial correlation statistic. Like the, partial correlation ,it is a measure of the correlation between two variables that remains after controlling for (i.e., "partialling" out) the effects of one or more other predictor variables. However, while the squared partial correlation between a predictor X1 and a response variable Y can be interpreted as the proportion of (unique) variance accounted for by X1, in the presence of other predictors X2, ... , Xk, relative to the residual or unexplained variance that cannot be accounted for by X2, ... , Xk, the squared semi-partial or part correlation is the proportion of (unique) variance accounted for by the predictor X1, relative to the total variance of Y. Thus, the semi-partial or part correlation is a better indicator of the "practical relevance" of a predictor, because it is scaled to (i.e., relative to) the total variability in the dependent (response) variable.
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