Essay
(Requires Appendix material)If the Gauss-Markov conditions hold,then OLS is BLUE.In addition,assume here that X is nonrandom.Your textbook proves the Gauss-Markov theorem by using the simple regression model Yi = β0 + β1Xi + ui and assuming a linear estimator .Substitution of the simple regression model into this expression then results in two conditions for the unbiasedness of the estimator:
= 0 and
= 1.
The variance of the estimator is var(
X1,…,Xn)=
.
Different from your textbook,use the Lagrangian method to minimize the variance subject to the two constraints.Show that the resulting weights correspond to the OLS weights.
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Define the Lagrangian as follows:
L =
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Correct Answer:
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L =
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