Does an UMVUE's variance match the Cramer-Rao lower bound?

1.2k Views Asked by At

I know it can match the CRLB, but does it have to, if it is an UMVUE?

1

There are 1 best solutions below

0
On BEST ANSWER

It doesn't have to. It does only if it is efficient. For example if $\{x_i\}_{i=1}^N$ is an i.i.d sequence such that $x_i \tilde~ N(\mu,\sigma^2) i=1,...,N$ where both $\mu,\sigma^2$ are unknown, then there exists no efficient estimator for $\sigma^2$, however $\hat\sigma^2=\frac{\sum_{i=1}^N(x_i-\overline{x})^2}{N-1}$ is a UMVUE.