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Explain how the tails of a test depend on the sign in the alternative hypothesis. Describe the signs in the null and alternative hypotheses for a two-tailed, a left-tailed, and a right-tailed test, respectively.

Short Answer

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Two-tailed test holds a hypothesis of \(H_0: \mu = \mu_0\) and \(H_a: \mu \neq \mu_0\). Left-tailed test holds \(H_0: \mu \geq \mu_0\) and \(H_a: \mu < \mu_0\). Right-tailed test holds \(H_0: \mu \leq \mu_0\) and \(H_a: \mu > \mu_0\). The sign in the alternative hypothesis determines the type (direction) of the tail in the test. Two-tailed tests look for departures on either side of the hypothesized parameter value while one-tailed tests look specifically for increases (right-tailed) or decreases (left-tailed) from the current state.

Step by step solution

01

Two-tailed test

Two-tailed tests are used when the alternative hypothesis does not specify the direction of the effect. Thus, for a two-tailed test, the null hypothesis \(H_0\) will usually have an equals sign, e.g. \(H_0: \mu = \mu_0\), and the alternative hypothesis \(H_1\) or \(H_a\) will typically involve a not equals sign, e.g. \(H_a: \mu \neq \mu_0\). This means we're interested in departures on either side of the hypothesized parameter value.
02

Left-tailed test

Left-tailed tests are used when the direction of the effect specified in the alternative hypothesis is 'less than'. Thus, for a left-tailed test, the null hypothesis \(H_0\) will usually be \(H_0: \mu \geq \mu_0\), and the alternative hypothesis \(H_a\) will be \(H_a: \mu < \mu_0\). Envision this as the test looking for a decrease from the current state.
03

Right-tailed test

Right-tailed tests are used when the direction of the effect specified in the alternative hypothesis is 'greater than'. Thus, for a right-tailed test, the null hypothesis \(H_0\) will usually be \(H_0: \mu \leq \mu_0\), and the alternative hypothesis \(H_a\) will be \(H_a: \mu > \mu_0\). In essence, this test is looking for an increase from the current state.

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