Consider the density data in Exercise 6-20.

(a) Estimate the mean density given that dielectric constant 

2.4 and loss factor  0.025.

(b) Compute a 95% CI on this mean response.

(c) Compute a 95% PI on a future observation at the same values of the regressors.

(d) What do you notice about the relative size of these two intervals?

Which is wider and why?