Question 6.15: Refer to Example 6.14. How many voters must be sampled so th...

Principles of Statistics for Engineers and Scientists

Refer to Example 6.14. How many voters must be sampled so that the power will be 0.8 when the true value of p = 0.55?

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The following computer output (from MINITAB) presents the solution:

Power and Sample Size

Test for One Proportion

Testing proportion = 0.5 (versus not = 0.5)

Alpha= 0.05

Alternative Sample Target

Proportion Size Power Actual Power

0.55 783 0.8 0.800239

The needed sample size is 783. Note that the actual power is slightly higher than 0.80. Because the sample size is discrete, it is not possible to find a sample size that provides exactly the power requested (the target power). So MINITAB calculates the smallest sample size for which the power is greater than that requested.

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