Critical Thinking Challenges
The power of a test can be calculated when a specific value of the mean is hypothesized in the alternative hypothesis. For example, let H0 = 50 and let H = 52. To find the power of a test, it is necessary to find the value of α. This can be done by the following steps:
Step 1: For a specific value of α, find the corresponding X-value of X using the formula X = H0 + Zασ/√n, where Zα is the critical value given in the hypothesis. Use a right-tailed test.
Step 2: Using the value of X found in step 1 and the value of σ in the alternative hypothesis, find the area corresponding to X in the Z-score formula Z = (X - H)/σ√n.
Step 3: Subtract this area from 0.5000. This is the value of β.
Step 4: Subtract the value of β from 1. This will give you the power of a test. See Figure 8-41.
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Answers to Applying the Concepts
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1. Find the power of a test using the hypotheses given previously and α = 0.05, σ = 3, and n = 30.
2. Select several other values for α in H and compute the power of the test. Generalize the results.
FIGURE 8-41: Relationship Among α and the Power of a Test
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