| Multiple Regression |
Residuals-by-Predicted Plot
SAS/INSIGHT software provides many diagnostic tools to help you decide if your regression model fits well. These tools are based on the residuals from the fitted model. The residual for the ith observation is the observed value minus the predicted value:
The plot of the residuals versus the predicted values is a classical diagnostic tool used in regression analysis. The plot is useful for discovering poorly specified models or heterogeneity of variance (Myers 1986, pp. 138 -139). The plot of R_GPA versus P_GPA in Figure 14.5 indicates no such problems. The observations are randomly scattered above and below the zero line, and no observations appear to be outliers.
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