Residual versus Leverage
If there are any influential points in the data, the Residual versus Leverage plot helps in identifying it. It's common to think that all outlier points are influential, that is, it decides how the regression line comes out. However, not all outliers are influential points. Even if a point is within a reasonable range of values (not an outlier), it could still be an influential point.
In the next plot, we will look out for far off values at the top-right corner or at the bottom-right corner. Those regions are the spaces where observation can be influential in contrast to a regression line. In Figure 4.7, the observations of the red dashed line with high Cook's distance are influential for the regression results. The regression results will be changed if we remove those observations. In the following figure, the bottom plot shows that observation 40 and 39 outside of the dashed line (high Cook's distance). Note that these observations are consistently appearing in...
