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Asymptotic Methods in Statistical Inference - Statistics Centre

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227<br />

By uniqueness of m.g.f.s,<br />

(; ) =<br />

(;0)<br />

R<br />

(;0)<br />

= (;0)<br />

()<br />

= {−()} (;0)<br />

Thus the density of <strong>in</strong>terest is<br />

(;0)= {−+()} (; ) <br />

(25.1)<br />

To get an accurate normal approximation at we<br />

choose such that the tilted sum has a mean of<br />

:<br />

= [ ; ] = (<br />

( + )<br />

= 0 () <br />

()<br />

Def<strong>in</strong>e ˆ by<br />

) <br />

|=0<br />

0 ³ˆ´ = (25.2)<br />

The normal approximation to the density of the<br />

tilted is<br />

à !<br />

1 − [<br />

(; ) ≈<br />

( ; ) ; ]<br />

<br />

( ; )

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