Using a Non-Constant Sample Size across Groups Example

This example uses the Failuressize.jmp sample data table, which contains failure data and a frequency column. It lists causes of failure during the fabrication of integrated circuits and the number of times each type of defect occurred for two processes. Among the other causes (Oxide Defect, Silicon Defect, and so on) is a cause labeled size. Specifying size as the cause code designates the rows as size rows.

Select Help > Sample Data Library and open Quality Control/Failuressize.jmp.

Select Analyze > Quality and Process > Pareto Plot.

Select Causes and click Y, Cause.

Select Process and click X, Grouping.

Select Count and click Freq.

Select Per Unit Analysis and then select Value in Freq Column.

Enter size in Cause Code.

Click OK.

Figure 12.12 Pareto Plot Report Window

Select Count Analysis > Per Unit Rates and Count Analysis > Test Rates Across Groups from the red triangle menu.

Figure 12.13 Per Unit Rates and Test Rates across Groups Results

Note that the sample size of 101 is used to calculate the DPU for the causes in group A. However, the sample size of 145 is used to calculate the DPU for the causes in group B.

If there are two group variables (say, Day and Process), Per Unit Rates lists DPU or rates for every combination of Day and Process for each cause. However, Test Rate Across Groups only tests overall differences between groups.