For the following instrumental variables (IV) regression model:
Yt = 3T xt + ut
Xt = TTWt + Vt
(4)
where E(ut|xt) = 0 and E(ut|wt) = 0. Here, it is assumed that wt is l x 1 and xt is k x 1 with l > k for identification. If l > k, model (4) is over-identified.
(a) Please derive the IV estimator for β, denoted by β̂.
(b) Show all steps on tests of over-identifying restrictions and the DWH Hausman test for model (4).