ROBUST TWO�STAGE LEAST SQUARES: SOME MONTE CARLO EXPERIMENTS

Abstract

The Two�Stage Least Squares (2�SLS) is a well known econometric technique used to estimate the parameters of a multi�equation econometric model when errors across the equations are not correlated and the equation(s) concerned is (are) over�identified or exactly identified. However, in presence of outliers in the data matrix, the classical 2�SLS has a very poor performance. In this study a method has been proposed to generalize the 2�SLS to the Weighted Two�Stage Least Squares (W2�SLS), which is robust to the effects of outliers and perturbations. Monte Carlo experiments have been conducted to demonstrate the performance of the proposed method. It has been found that robustness of the proposed method is not much destabilized by the magnitude of outliers. The breakdown point of the method is quite high, somewhere between 45 to 50 percent of the number of points in the data matrix.Two�Stage Least Squares, multi�equation econometric model, simultaneous equations, outliers, robust, weighted least squares, Monte Carlo experiments, unbiasedness, efficiency, breakdown point, perturbation, structural parameters, reduced form