2. Suppose E(X1) = E(X2) = , Var(X) =4, Var(X2) = 9 and Cov(X1,X2) =1. Your goal is to estimate the unknown mean .
(a) Consider an unbiased estimator of the form: = X + (1 - )X2. What value should be chosen for the constant in order to minimize the mean squared error of ?
(b) What is the relative efficiency of (for the value of you found) with respect to the estimator o = X1?