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Asymptotic Methods in Statistical Inference - Statistics Centre

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179<br />

• Information Inequality. (Cramér-Rao Inequality.)<br />

Assume (C1) - (C6). Let (X) beanunbiased<br />

estimator of (), so that<br />

() =<br />

Z<br />

(x) (|x) x<br />

Then, assum<strong>in</strong>g that the follow<strong>in</strong>g <strong>in</strong>terchange of<br />

operations is permissible (the ma<strong>in</strong> requirement<br />

is the cont<strong>in</strong>uity, <strong>in</strong> , of the <strong>in</strong>tegrand and of its<br />

absolute value, after differentiat<strong>in</strong>g),<br />

Z<br />

0 () = (x) 0 (|x)<br />

(|x) x<br />

(|x)<br />

"<br />

#<br />

log (|X)<br />

= (X)<br />

<br />

"<br />

#<br />

log (|X)<br />

= (X) <br />

<br />

Then<br />

h<br />

0 () i 2 log (|X)<br />

≤ [(X)] "<br />

<br />

= [(X) − ()] · ()<br />

h√ i<br />

= ((X) − ()) · () <br />

#

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