This problem uses the data from Problem 15 in Chapter 5.
a. Using a computer program, fit a cubic polynomial model with BLOODTOL as the response and PPM_TOLU as the predictor. Center PPM_TOLU. Provide the prediction equation.
b.-e. Repeat parts (b) through (e) from Problem 8 for this analysis.
f. Compute the estimated variance for each estimated regression coefficient. Are these estimates approximately equal?
g. Compare the results obtained here to those obtained in Chapter 5.
In Problem 8
b. Using variables-added-in-order tests, determine the best model.
c. Report variables-added-last tests. Explain any differences between your results here and those you obtained in part (b).
d. Report appropriate collinearity diagnostics for the model, and evaluate them. Include predictor correlations.
e. Plot jackknife (or studentized) residuals against predicted values for the best model based on your results in part (b). Provide a frequency histogram or schematic plot of the residuals, and comment on it.