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Consider a random sample \(X_{1}, X_{2}, \ldots, X_{n}\) from a distribution with pdf \(f(x ; \theta)=\theta(1-x)^{\theta-1}, 00\) (a) Find the form of the uniformly most powerful test of \(H_{0}: \theta=1\) against \(H_{1}: \theta>1\) (b) What is the likelihood ratio \(\Lambda\) for testing \(H_{0}: \theta=1\) against \(H_{1}: \theta \neq 1 ?\)

Short Answer

Expert verified
For part (a), the rule will have the form \(Reject H_0: \theta =1 if \frac{1-n}{s} > k\), where \(s\) is the sample mean. The likelihood ratio for part (b) would be \(\Lambda = \frac{1}{(\theta(1-x)^{\theta-1})}\).

Step by step solution

01

Writing Down the Likelihood Function

The likelihood function can be given as \(L(\theta; x) = \prod_{i=1}^{n} \theta(1-x_i)^{\theta-1}\). Notice that likelihood function is a function of \(\theta\) given the observed sample.
02

Deriving the Uniformly Most Powerful Test

The Neyman-Pearson lemma states that the most powerful test for testing \(H_0: \theta = \theta_0\) against \(H_1: \theta = \theta_1\) has a critical region defined by \{x : \frac{f(x|\theta_1)}{f(x|\theta_0)} > k \} where \(k\) a constant depending on the size of the test. Applying this to our hypotheses, the rejection rule becomes \(\frac{(1-x)^0}{(1-x)} > k\). Solve for \(k\), this gives us the uniformly most powerful test.
03

Calculating the Likelihood Ratio

For the likelihood ratio test, we need to compute the ratio \( \Lambda = \frac{L(\theta_0)}{L(\theta_1)} \). This can be computed by substituting \(\theta = 1\) and \(\theta \neq 1\) in the derived likelihood function.

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Most popular questions from this chapter

If \(X_{1}, X_{2}, \ldots, X_{n}\) is a random sample from a distribution having pdf of the form \(f(x ; \theta)=\theta x^{\theta-1}, 0

Consider a normal distribution of the form \(N(\theta, 4)\). The simple hypothesis \(H_{0}: \theta=0\) is rejected, and the alternative composite hypothesis \(H_{1}: \theta>0\) is accepted if and only if the observed mean \(\bar{x}\) of a random sample of size 25 is greater than or equal to \(\frac{3}{5}\). Find the power function \(\gamma(\theta), 0 \leq \theta\), of this test.

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Let \(X_{1}, \ldots, X_{n}\) and \(Y_{1}, \ldots, Y_{m}\) follow the location model $$\begin{aligned} X_{i} &=\theta_{1}+Z_{i}, \quad i=1, \ldots, n \\ Y_{i} &=\theta_{2}+Z_{n+i}, \quad i=1, \ldots, m\end{aligned}$$ where \(Z_{1}, \ldots, Z_{n+m}\) are iid random variables with common pdf \(f(z)\). Assume that \(E\left(Z_{i}\right)=0\) and \(\operatorname{Var}\left(Z_{i}\right)=\theta_{3}<\infty\) (a) Show that \(E\left(X_{i}\right)=\theta_{1}, E\left(Y_{i}\right)=\theta_{2}\), and \(\operatorname{Var}\left(X_{i}\right)=\operatorname{Var}\left(Y_{i}\right)=\theta_{3}\). (b) Consider the hypotheses of Example \(8.3 .1\); i.e, $$H_{0}: \theta_{1}=\theta_{2} \text { versus } H_{1}: \theta_{1} \neq \theta_{2}$$ Show that under \(H_{0}\), the test statistic \(T\) given in expression \((8.3 .5)\) has a limiting \(N(0,1)\) distribution. (c) Using Part (b), determine the corresponding large sample test (decision rule) of \(H_{0}\) versus \(H_{1}\). (This shows that the test in Example \(8.3 .1\) is asymptotically correct.)

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