Section 4.1

Introduction

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Problem 4.1.1

Verify the expressions for π(λ∣xˉ)\pi (\lambda \mid \bar{x}) and δk(xˉ)\delta^{k}(\bar{x}) in Example 1.3.

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Problem 4.1.2

Give examples of pairs of values (a,b)(a, b) for which the beta density B(a,b)B(a, b) is

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(a)

decreasing,

(b)

increasing,

(c)

increasing for p<p0p<p_{0} and decreasing for p>p0p>p_{0}, and

(d)

decreasing for p<p0p<p_{0} and increasing for p>p0p>p_{0}.

Problem 4.1.3

In Example 1.5, if pp has the improper prior density 1p(1−p)\frac{1}{p(1-p)}, show that the posterior density of pp given xx is proper, provided 0<x<n0<x<n.

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Problem 4.1.4

In Example 1.5, find the Jeffreys prior for pp and the associated Bayes estimator δΛ\delta_{\Lambda }.

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Problem 4.1.5

For the estimator δΛ\delta_{\Lambda } of Problem 1.4,

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(a)

calculate the bias and maximum bias;

(b)

calculate the expected squared error and compare it with that of the UMVU estimator.

Problem 4.1.6

In Example 1.5, find the Bayes estimator δ\delta of p(1−p)p(1-p) when pp has the prior B(a,b)B(a, b).

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Problem 4.1.7

For the situation of Example 1.5, the UMVU estimator of p(1−p)p(1-p) is δ′=[x(x−1)]/[n(n−1)]\delta^{\prime }=[x(x- 1)] /[n(n-1)] (see Example 2.3.1 and Problem 2.3.1).

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(a)

Compare the estimator δ\delta of Problem 1.6 with the UMVU estimator δ′\delta^{\prime }.

(b)

Compare the expected squared error of the estimator of p(1−p)p(1-p) for the Jeffreys prior in Example 1.5 with that of δ′\delta^{\prime }.

Problem 4.1.8

In analogy with Problem 1.2, determine the possible shapes of the gamma density Γ(g,1/α),α,g>0\Gamma (g, 1 / \alpha ), \alpha , g>0.

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Problem 4.1.9

Let X1,…,XnX_{1}, \ldots , X_{n} be iid according to the Poisson distribution P(λ)P(\lambda ) and let λ\lambda have a gamma distribution Γ(g,α)\Gamma (g, \alpha ).

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(a)

For squared error loss, show that the Bayes estimator δα,g\delta_{\alpha , g} of λ\lambda has a representation analogous to (1.1.13).

(b)

What happens to δα,g\delta_{\alpha , g} as (i) n→∞n \rightarrow \infty, (ii) α→∞,g→0\alpha \rightarrow \infty , g \rightarrow 0, or both?

Problem 4.1.10

For the situation of the preceding problem, solve the two parts corresponding to Problem 1.5(a) and (b).

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Problem 4.1.11

In Problem 1.9, if λ\lambda has the improper prior density dλ/λd \lambda / \lambda (corresponding to α=g=\alpha =g= 0 ), under what circumstances is the posterior distribution proper?

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Problem 4.1.12

Solve the problems analogous to Problems 1.9 and 1.10 when the observations consist of a single random variable XX having a negative binomial distribution Nb(p,m)N b(p, m), pp has the beta prior B(a,b)B(a, b), and the estimand is

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(a)

pp and

(b)

1/p1 / p.