(10) = {01²-¹0 0, elsewhere. a Show that this density function is in the (one-parameter) exponential family and that -In(Y) is sufficient for 9. (See Exercise 9.45.) b If W₁ = -In(Y), show that W, has an exponential distribution with mean 1/0. c Use methods similar to those in Example 9.10 to show that 20 with 2n df. W, has a x² distribution

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Answer 9.60

**9.45**

Suppose that \( Y_1, Y_2, \ldots, Y_n \) is a random sample from a probability density function in the (one-parameter) exponential family so that

\[
f(y \mid \theta) = 
\begin{cases} 
a(\theta)b(y)e^{-[c(\theta)d(y)]}, & a \leq y \leq b, \\
0, & \text{elsewhere},
\end{cases}
\]

where \( a \) and \( b \) do not depend on \(\theta\). Show that \(\sum_{i=1}^n d(Y_i)\) is sufficient for \(\theta\).
Transcribed Image Text:**9.45** Suppose that \( Y_1, Y_2, \ldots, Y_n \) is a random sample from a probability density function in the (one-parameter) exponential family so that \[ f(y \mid \theta) = \begin{cases} a(\theta)b(y)e^{-[c(\theta)d(y)]}, & a \leq y \leq b, \\ 0, & \text{elsewhere}, \end{cases} \] where \( a \) and \( b \) do not depend on \(\theta\). Show that \(\sum_{i=1}^n d(Y_i)\) is sufficient for \(\theta\).
**Exercise 9.60**

Let \( Y_1, Y_2, \ldots, Y_n \) denote a random sample from the probability density function

\[
f(y \mid \theta) =
\begin{cases} 
    \theta y^{\theta - 1}, & 0 < y < 1, \, \theta > 0, \\
    0, & \text{elsewhere}.
\end{cases}
\]

**a.** Show that this density function is in the (one-parameter) exponential family and that \( \sum_{i=1}^{n} -\ln(Y_i) \) is sufficient for \( \theta \). (See Exercise 9.45.)

**b.** If \( W_i = -\ln(Y_i) \), show that \( W_i \) has an exponential distribution with mean \( 1 / \theta \).

**c.** Use methods similar to those in Example 9.10 to show that \( 2\theta \sum_{i=1}^{n} W_i \) has a \(\chi^2\) distribution with \( 2n \) degrees of freedom.

**d.** Show that

\[
E \left( \frac{1}{2\theta \sum_{i=1}^{n} W_i} \right) = \frac{1}{2(n-1)}.
\]

[Hint: Recall Exercise 4.112.]

**e.** What is the MVUE for \( \theta \)?
Transcribed Image Text:**Exercise 9.60** Let \( Y_1, Y_2, \ldots, Y_n \) denote a random sample from the probability density function \[ f(y \mid \theta) = \begin{cases} \theta y^{\theta - 1}, & 0 < y < 1, \, \theta > 0, \\ 0, & \text{elsewhere}. \end{cases} \] **a.** Show that this density function is in the (one-parameter) exponential family and that \( \sum_{i=1}^{n} -\ln(Y_i) \) is sufficient for \( \theta \). (See Exercise 9.45.) **b.** If \( W_i = -\ln(Y_i) \), show that \( W_i \) has an exponential distribution with mean \( 1 / \theta \). **c.** Use methods similar to those in Example 9.10 to show that \( 2\theta \sum_{i=1}^{n} W_i \) has a \(\chi^2\) distribution with \( 2n \) degrees of freedom. **d.** Show that \[ E \left( \frac{1}{2\theta \sum_{i=1}^{n} W_i} \right) = \frac{1}{2(n-1)}. \] [Hint: Recall Exercise 4.112.] **e.** What is the MVUE for \( \theta \)?
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