Select the method or formula of your choice.

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 |
---|---|

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.) |