Consider the HFE data and multiple linear regression model in Exercise 6-22.

(a) Find the mean HFE given that x1  14.5, x2  220, and x3  5.0.

(b) Compute a 90% CI on this mean response.

(c) Compute a 90% PI on a future observation when x1  14.5, x2  220, and x3  5.0.

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

Which is wider and why?