Publication date: 08/13/2020

Example of the Two Sample Proportions Calculator

Suppose you are responsible for two silicon wafer assembly lines. Based on the knowledge from many runs, one of the assembly lines has a defect rate of 8% and the other line has a defect rate of 6%. You want to know the sample size necessary to have 80% power to conclude there is a difference in defect rates.

1. Select DOE > Design Diagnostics > Sample Size and Power.

2. Click Two Sample Proportions.

3. Leave Alpha set at 0.05.

4. Enter 0.08 for Proportion 1.

5. Enter 0.06 for Proportion 2.

6. Select a Two-Sided test.

7. Enter 0 for Null Difference in Proportion.

8. Leave Sample Size 1 and Sample Size 2 blank.

9. Enter 0.8 for Power.

10. Click Continue.

Figure 17.13 Difference between Two Proportions for a Two-Sided Test 

The calculator shows that you should test a sample size of 2,554 wafers from each production line in order to detect a difference in defect rates.

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