Select the method or formula of your choice.

Each data point, s*i*, is the standard deviation of subgroup, *i*.

The center line represents the average standard deviation for a subgroup.

If you do not use an unbiasing constant, then Minitab uses the process standard deviation, *σ*:

If you use an unbiasing constant(default), then Minitab calculates the center line value for each subgroup, *i*, as follows:

Term | Description |
---|---|

σ | process standard deviation |

c_{4}() | value of the unbiasing constant c_{4} that corresponds to the value that is specified in parentheses. |

n_{i} | number of observations in subgroup i |

If you do not specify a historical value for the process standard deviation, *σ*, then Minitab estimates *σ* from your data using the specified method.

If the unbiasing constant is used:

If the unbiasing constant is not used:

If the unbiasing constant is used:

If the unbiasing constant is not used:

Term | Description |
---|---|

c_{4}() | value of the unbiasing constant c_{4} that corresponds to the value that is specified in parentheses. |

n_{i} | number of observations in subgroup i |

σ | process standard deviation |

c_{5}() | value of the unbiasing constant c_{5} that corresponds to the value that is specified in parentheses. |

k | parameter for Test 1. The default is 3. |