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Abstract
In dynamic panel models, the generalized method of moments (GMM) has been used in many applications since it gives efficient estimators. This efficiency is affected by the choice of the initial weight matrix. It is common practice to use the inverse of the moment matrix of the instruments as an initial weight matrix. However, an initial optimal weight matrix is not known, especially in the system GMM estimation procedure. Therefore, we present the optimal weight matrix for level GMM estimator, and suboptimal weight matrices for system GMM estimator, and use these matrices to increase the efficiency of GMM estimator. Using the Kantorovich inequality (KI), we find that the potential efficiency gain becomes large when the variance of individual effects increases compared to the variance of the errors