Note that the first order conditions for GMM take the following form: G for some matrix . We could estimate φ by using some first stage estimator of G instead of W and solving the equation which will result in an estimator that is asymptotically equivalent to GMM. The central idea of MEF is to use a more general form PT. The problem that MEF solves is formulated as a weighted sum of the matringale differences: wtmt and at the true parameter values MT (φ) = 0. The MEF estimator φbMEF solves for some optimal set of weights wt
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