Consider the multiple regression of y on K variables X and an additional variable z. Prove that

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Consider the multiple regression of y on K variables X and an additional variable z. Prove that under the assumptions A1 through A6 of the classical regression model, the true variance of the least squares estimator of the slopes on X is larger when z is included in the regression than when it is not. Does the same hold for the sample estimate of this covariance matrix? Why or why not? Assume that X and z are nonstochastic and that the coefficient on z is nonzero.

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Econometric Analysis

ISBN: 978-0131395381

7th edition

Authors: William H. Greene

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