Sargan’s generalized
IV estimator (GIVE) provided an asymptotically efficient technique for using surplus
instruments in the application of the IV method to econometric problems, and formed
the basis of subsequent developments of the generalized method of moments (GMM)
estimators introduced subsequently by Hansen (1982). A related class of estimators,
known as k-class estimators, was also proposed by Theil (1958). Methods of estimating
the entire system of equations which were computationally less demanding than the FIML
method were also advanced. These methods also had the advantage that unlike the FIML
did not require the full specification of the entire system.