Use the data in FERTIL3.RAW for this exercise.
(i) Add pe t-3 and pet-4 to equation (10.19). Test for joint significance of these lags.
(ii) Find the estimated long-run propensity and its standard error in the model from part (i). Compare these with those obtained from equation (10.19).
(iii) Estimate the polynomial distributed lag model from Problem 10.6. Find the estimated LRP and compare this with what is obtained from the unrestricted model.