Design of Experiments Guide  • Prospective Sample Size and Power • One Sample Proportion Calculator • Example of the One Sample Proportion Calculator

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Example of the One Sample Proportion Calculator
Suppose that an assembly line has a historical proportion of defects equal to 0.1. You want to know the power to detect that the proportion is different from 0.2, given an alpha level of 0.05 and a sample size of 100.
1.
Select DOE > Design Diagnostics > Sample Size and Power.
2.
Click One Sample Proportion.
3.
Leave Alpha as 0.05.
4.
Leave 0.1 as the value for Proportion.
5.
Leave the Method as Exact Agresti-Coull.
6.
Leave the test type as Two-Sided.
7.
Leave 0.2 as the value for Null Proportion.
8.
Enter 100 as the Sample Size.
9.
Click Continue.
Figure 17.12 One Sample Proportion Calculator
For a sample size of 100, the power is approximately 70%. The Actual Test Size is approximately 0.0467, which is slightly less than the desired 0.05. With a sample size of 100, if the defect rate is 0.2, the probability of a Type I error of rejecting the null hypothesis is 5%. Alternatively, the probability of a Type II error of not rejecting the null hypothesis is 30% (1 - power).

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Help created on 3/19/2020