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?