Consider the regression model fit to the grey range modulation data in Exercise 12-15.

Use the useful range as the response.

(a) What proportion of total variability is explained by this model?

(b) Construct a normal probability plot of the residuals. What conclusion can you draw from this plot?

(c) Plot the residuals versus and versus each regressor, and comment on model adequacy.

(d) Calculate Cook’s distance for the observations in this data set. Are there any influential points in these data?