11.6. Refer to the previous exercise.

(a) Show how to obtain /^-squared from the sums of squares in the ANOVA table. Interpret it.

(b) r 2

= 0.78 when GDP is the sole predictor.

Why do you think K 2

does not increase much when cell-phone use is added to the model, even though it is itself highly associated with y (with r = 0.67)? {Hint: Would you expect x\

and X2 to be highly correlated? If so, what's the effect?)