11.26. Refer to the previous exercise.

(a) Find the partial correlation between y and x\, controlling for X2. Interpret the partial correlation and its square.

(b) Find the estimate of the conditional standard deviation, and interpret its value.

(c) Show how to find the estimated standardized regression coefficient for xi using the unstandardized estimate and the standard deviations, and interpret its value.

(d) Write the prediction equation using standardized variables. Interpret.

(e) Find the predicted z-scorc for a country that is one standard deviation above the mean on both predictors. Interpret.