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Example 5.11<br />

We poll n voters and record the fraction M n of those polled who are<br />

in favor of a particular candidate. If p is the fraction of the entire<br />

voter population that supports this candidate, then<br />

M n = X 1 + · · · + X n<br />

,<br />

n<br />

where X i ’s are i.i.d. Bernoulli random variables with parameter p.<br />

When n is large,<br />

M n − p = X 1 + · · · + X n − np<br />

n<br />

= X 1 + · · · + X n − np<br />

√ nσ<br />

= Z n<br />

) ≈ Y ).<br />

( √n<br />

( √n<br />

σ √n<br />

σ<br />

σ<br />

Chia-Ping Chen ( 中 山 資 工 ) Limit Theorems 機 率 學 講 義 27 / 28

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