6. Let X1, X2, ..., X'n be iid from N(u, G). It is known that that $2 = - 1 (X; - X)2 is an unbiased estimator of o', and that Var [$2 ] = 20 n - 1 i=1 n - 1 n Let of ( X , - X ) 2 = n - 1 $2 be another estimator of o2. n n i=1 Find the mean square error MSE of 67