Refer to the previous exercise. Use backward elimination to select a model.

a. Use an initial model containing the two-factor interactions. When you reach the stage at which all terms are statistically significant, adjusted R2 should still be about 0.87. See whether you can simplify further without serious loss of practical significance. Interpret your final model.

b. A simple model for these data has only main effects for size, new, and taxes. Compare your model with this model in terms of adjusted R2, AIC, and the summaries of effects.

c. If any observations seem to be influential, redo the analyses to analyze their impact.