Interesting and very clear, as usual, thanks a lot, Rick! Does this method apply in case of specification error (eg when the partial leverage plot exhibits a curvilinear pattern for some X, suggesting to re-specific the model after adding a quadratic term, X²)? I am also wondering about the added value of this graphical tool over the t-value of each regression coefficient which is displayed by the default output of PROC REG. Maybe, while they both tools (analytic and graphical) test for the same H0, one could take advantage (but how?) of the fact that instead of being limited to one figure (the t value), a partial leverage plot offers a multi-points insight. Anyway, thanks for your always stimulating posts on the Do Loop! Jean-Claude