Mathematical Statistics with Applications
Mathematical Statistics with Applications
7th Edition
ISBN: 9781111798789
Author: Dennis O. Wackerly
Publisher: Cengage Learning
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Chapter 14.3, Problem 6E

a.

To determine

Obtain the expression E(ninj).

a.

Expert Solution
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Explanation of Solution

In this context, it is assumed that the assumptions associated with a multinomial experiment are all satisfied. Based on Section 5.9, each of the ni's,i=1,2,...,k follows binomial distribution with parameters nandpi. Further, Cov(ni,nj)=npipjifij.

The value of the expression E(ninj) is given below:

E(ninj)=E(ni)E(nj)=npinpj=n(pipj)

b.

To determine

Provide the unbiased estimator of (pipj) with reference to Part (a).

b.

Expert Solution
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Explanation of Solution

From Part (a), E(ninj)=n(pipj).

Then,

E(ninjn)=1nE(ninj)=1n(E(ni)E(nj))=1n(npinpj)=pipj

An unbiased estimator for θ=pipj is given below:

θ^=ninjn

c.

To determine

Verify that V(ninj)=n[pi(1pi)+pj(1pj)+2pipj].

c.

Expert Solution
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Explanation of Solution

It is known that Cov(ni,nj)=npipjifij. Also, the variance of a linear combination is given below:

V(aX+bY)=V(aX)+V(bY)+2Cov(aX,bY)=a2V(X)+b2V(Y)+2abCov(X,Y)

Now,

V(ninj)=V(ni)+V(nj)+2Cov(ni,nj)=V(ni)+(12)V(nj)+2(1)Cov(ni,nj)=V(ni)+V(nj)2Cov(ni,nj)=npi(1pi)+npj(1pj)2(npipj)=npi(1pi)+npj(1pj)+2npipj=n[pi(1pi)+pj(1pj)+2pipj]

Hence, it has been verified that V(ninj)=n[pi(1pi)+pj(1pj)+2pipj].

d.

To determine

Obtain the variance of unbiased estimator with reference to Part (c).

d.

Expert Solution
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Explanation of Solution

From Part (a), E(ninj)=n(pipj).

Then,

V(ninjn)=1n2V(ninj)=1n2[V(ni)+V(nj)+2Cov(ni,nj)]=1n2[V(ni)+(12)V(nj)+2(1)Cov(ni,nj)]=1n2[V(ni)+V(nj)2Cov(ni,nj)]=1n2[npi(1pi)+npj(1pj)+2npipj]=1n2[n[pi(1pi)+pj(1pj)+2pipj]]=1n[pi(1pi)+pj(1pj)+2pipj]

e.

To determine

Obtain the consistent estimator of n1V(ninj).

e.

Expert Solution
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Explanation of Solution

A consistent estimator for n1V(ninj) is p^ip^j because it is an unbiased estimator and variance reaches at 0 as n increases.

f.

To determine

Verify that a large sample (1α)100% confidence interval for pipj is given below: p^ip^j±zα2pi(1pi)+pj(1pj)+2pipjn.

f.

Expert Solution
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Explanation of Solution

It is known that the variable Hn=p^ip^jpi+pj1n[pi(1pi)+pj(1pj)+2pipj] has normal distribution.

Since pi and pj are consistent estimators, then σp^ip^jσ^p^ip^j tends to 0.

Now,

Hnσp^ip^jσ^p^ip^j=p^ip^jpi+pj1n[pi(1pi)+pj(1pj)+2pipj] has the limiting standard deviation.

In this context, it has been showed that a transformation of Hn has a standard normal distribution.

Therefore, (1α)100% confidence interval for pipj is given by: p^ip^j±zα2pi(1pi)+pj(1pj)+2pipjn

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Mathematical Statistics with Applications

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