STAB22H3 Chapter 9: Chapter 9.docx
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STAB22H3 Full Course Notes
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Plotting the residuals or creating a histogram of residuals can reveal groups of data with the overall set of data. Points whose residuals are large always deserve special attention. A point has high leverage if its x-value is far from the mean of the x-values; they pull strongly on the regression line. A point with high leverage has the potential to change the regression line. To see if a high leverage point changes the model, fit the linear model both with and without the point a point is influential if omitting it from the analysis gives a very different model. The best way to identify unusual cases is against the background of a model, but good models should not be unduly influenced by a small number of unusual cases.
