Question: Compute the leverage values for the data in Exercise 13.12. What outliers are suggested by the leverages?
Exercise: The following data were given in U.S. Environmental Protection Agency (1978) and also discussed by Stromberg (1993). The objective was to develop a regression model that relates the mean annual total nitrogen concentration (TN) to the average influent nitrogen concentration (NIN) and the water retention time (TW).
Fit the model TN = NINA' + α74β) + ?, as suggested by the EPA investigator, then compute R2, using the computational formula in Section 13.3. Then compute R2 as . Which result is preferable, at least for this problem? Construct dot pilots for NIN, TN, and TW. Do the dot plots suggest that there are any outliers? If there are any obvious outliers, delete them and recompute the regression equation. If you deleted any outliers, does your new regression equation appear to adequately fit the data? Could a better fit be obtained with a linear regression equation?