Let \(X_1,X_2,\ldots ,X_n\) be independent identically distributed Poisson random variables with common probability mass function \[ p(k,\theta )=\frac {\theta ^k}{k!}e^{-\theta },\qquad k=0,1,\ldots \] Using the Cramer-Rao inequality show that the sample mean is a uniformly minimum variance unbiased estimator for \(\theta \).