Minitab plots the number of defectives in each subgroup, .
If you do not specify a historical value for the process proportion (), then Minitab uses the average proportion of defectives from your data, , to estimate :
The location of the center line for each subgroup, , is calculated as follows:
Term | Description |
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size of subgroup | |
process proportion |
The LCL for each subgroup is the greater of the following:
The UCL for each subgroup is the lesser of the following:
Term | Description |
---|---|
size of subgroup | |
process proportion | |
parameter for Test 1. The default is 3. (For more information go to Select tests for special causes for NP Chart.) |