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Asymptotic Methods in Statistical Inference - Statistics Centre

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83<br />

• A strong CI on a population median. Suppose<br />

1 are a sample from , with unique median<br />

= −1 (5). (Here is viewed as a nuisance<br />

parameter.) Recall that the sample median<br />

ˆ is ³ 1 ³ 4 2 ()´´, but a CI based on<br />

this requires a knowledge of . Consider <strong>in</strong>stead<br />

the follow<strong>in</strong>g procedure based on the b<strong>in</strong>omial distribution.<br />

We test = 0 (2-sided) us<strong>in</strong>g the sign<br />

test, with test statistic<br />

( 0 ) = # of observations which are 0 <br />

We accept if ≤ ( 0 ) ≤ − .Notethat<br />

= − ⇔ obs’ns are ≤ 0 ⇔ 0 ∈ [ () (+1) )<br />

so that<br />

⇔<br />

≤ ( 0 ) ≤ − <br />

0 ∈∪ − <br />

= <br />

[ () (+1) )=[ ( ) (− +1) )<br />

Under , ∼ ( 12); thus 2 √ ³ <br />

Φ and we determ<strong>in</strong>e by requir<strong>in</strong>g that<br />

⎛<br />

⎝ 2√ ³ − 1 ´ √ ³<br />

2 ≤ 2 <br />

≤ 2 √ ³ − <br />

<br />

− 1 ´<br />

2<br />

→ 1 − <br />

<br />

− 1 2<br />

<br />

− 1 2<br />

´<br />

⎞<br />

⎠<br />

´ →

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