Question: Refer again to the Species data.

(a) Create two new variables, LnBody—which is the natural log of BodyWeight and LnBrain—which is the natural log of BrainWeight. Obtain a scatterplot of LnBrain against LnBody. Comment on the relationship between these two new variables. How does this graph compare with the one you obtained in the last question?

(b) Obtain the regression line relating LnBrain to LnBody, saving the leverages, the studentized deleted residuals, and the Cook’s distances. Comment on the values of these three measures for the three ‘unusual’ species.

(c) Use the regression line you obtained in part (b) to predict the brain weight for an adult horse. The average weight of an adult horse is 450 kilograms.

(d) Check the validity of the three conditions for inference in your model in part (b).