Compare the GLS estimator of SD

(a) in equation (9.51) to the OLS estimator calculated in equation (9.9).

(a) Which is larger?

(b) What must be true of the GLS estimator of SD

(a) in comparison to the true OLS value for SD(a)?

(c) What does this imply about the OLS estimator of SD

(a) calculated in equation (9.9)? Is it lower or higher than the true OLS value? Would the Newey-West autocorrelation-consistent estimate of SD

(a) be higher or lower than the calculated estimate in equation (9.9)?