Partial regression plots are related to, but distinct from, partial residual plots. Partial regression plots are most commonly used to identify leverage points and influential data points that might not be leverage points. Partial residual plots are most commonly used to identify the nature of the relationship between Y and Xi (given the effect of the other indpendent variables in the model). Note that since the simple correlation betweeen the two sets of residuals plotted is equal to the partial correlation between the response variable and Xi partial regression plots will show the correct strength of the linear relationship between the response variable and Xi This is not true for partial residual plots. On the other hand, for the partial regression plot, the x axis is not Xi. This limits its usefulness in determining the need for a transformation (which is the primary purpose of the partial residual plot)