Improving trees In the last exercise, you saw that the linear model had some deficiencies. Let’s create a better model.

1. Perhaps the cross-sectional area of a tree would be a better predictor of its age. Since area is measured in square units, try re-expressing the data by squaring the diameters. Does the scatterplot look better?

2. Create a model that predicts Age from the square of the Diameter.

3. Check the residuals plot for this new model. Is this model more appropriate? Why?

4. Estimate the age of a tree 18 inches in diameter.