Abstract:
For the system of two seemingly unrelated regression equations:
Yi=
Xiβi+
δi(
i=1,2), a new method of estimating
βi’s is introduced in this paper. Theestimator of
β1 is given as\beta_1^*(K)=\left(X_1^\prime X_1\right)^-1 X_1^\prime Y_1-\frac\sigma_12\sigma_22\left(X_1^\prime X_1\right)^-1 X_1 N_2 Y_2-K \frac\sigma_12^2\sigma_11 \sigma_22\times\left(X_1^\prime X_1\right)^-1 X_1^\prime P_2 Y_1, where
K is an arbitrary constant. The unrestricted two-step estimator, which is the feasible counterpart to
β1*(
K), is denoted as
β1*(
K,
T). In particular,
β1*(1)=\widetilde\beta_1, the covariance improved estimator introduced in 1, and
β1*(1)=\widetilde\beta_1, a biased estimator introduced in 2. It is shown that choosing a reasonable
K, the estimator
β1*(
K) may work better than\widetilde\beta_1, and
β1*(
K,
T) may perform better than \widetilde\beta_1(T), with respect to the mean square error matrix (MSEM) criterion. How to choose the optimal value of
K is also discussed.