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Asymptotic Methods in Statistical Inference - Statistics Centre

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36<br />

• Example: Let be ( ), so that =<br />

=ˆ is ( (1 − )). This is <strong>in</strong>convenient<br />

for mak<strong>in</strong>g <strong>in</strong>ferences about . To get<br />

confidence <strong>in</strong>tervals on we can <strong>in</strong>stead use the<br />

fact (which you should now be able to show) that<br />

√ ( − )<br />

q<br />

ˆ(1 − ˆ)<br />

<br />

→ (0 1)<br />

lead<strong>in</strong>g to CIs ‘ ± 2<br />

qˆ(1 − ˆ)’. A more<br />

accurate method is to use a variance stabiliz<strong>in</strong>g<br />

transformation.<br />

q<br />

Wechoose(·)sothat‘ 0 ()’=<br />

(1 − ) 0 () is <strong>in</strong>dependent of :<br />

0 () ∝<br />

1<br />

q(1 − ) ⇒ () ∝ arcs<strong>in</strong> √ <br />

S<strong>in</strong>ce ³ arcs<strong>in</strong> √ ´0<br />

= √ 1<br />

we have<br />

2 (1−)<br />

arcs<strong>in</strong><br />

qˆ ∼ (arcs<strong>in</strong> √ 1<br />

4 )<br />

From this we get CIs on arcs<strong>in</strong> √ ,andtransform<br />

them to get CIs on which are typically more<br />

accurate than those above.

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