topic Interpretation of leverage plots in Discussions

Interpretation of leverage plots

HarriBradbeer — Fri, 09 Jun 2023 00:37:01 GMT

Compare the model leverage plots below. In the first, the x-values are being offset from their actual values, which is not happening in the second.

The only difference between the two is that I've changed one number - table attached. The 214 in Factor 2 become 185 so that the two leftmost and two rightmost x-values in each plot are equal.

From reading the help guides I'm guessing the offset is something to do with the increased mean, but I don't understand why this affects the points in Factor 1, nor why the two leftmost points of Factor 2 are offset by different amounts (one +ve, one -ve) when they are equivalent. It seems to be artificially improving the model.

Any help that can be offered is much appreciated.

Re: Interpretation of leverage plots

Dan_Obermiller — Tue, 03 Aug 2021 17:08:37 GMT

Maybe this thread will help. It explains how the leverage plots are created.

Re: Interpretation of leverage plots

statman — Mon, 02 Aug 2021 20:04:40 GMT

The explanations of Leverage plots Dan posted above are pretty good. The thing you have to remember is these are plots of residuals. So changing data points don't reflect directly on these plots. A new model is created with the new data points and then new residuals are calculated.

Re: Interpretation of leverage plots

arooqi — Mon, 02 Aug 2021 21:40:12 GMT

You're creating a multiple regression model where the value of one variable affects on the prediction of the whole model. Changing the value of one factor with holding the response fixed will definitely change the CI of the factors.