Select the method or formula of your choice.

where:

* Z _{i}*, the MEWMA vector, represents the weighting of previous subgroups.

where:

*X _{i}*, the subgroup mean vector, =

= the weighted covariance matrix

where:

S is the sample covariance matrix. For more information on calculating the S matrix, go to Tsquared plotted point.

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

n | subgroup size |

S | sample covariance matrix. For more information on calculating the S matrix, see T-squared statistic |

The program used to calculate the upper control limit for the MEWMA chart is described in Bodden et al.^{1}

If you use a Box-Cox transformation, Minitab transforms the original data values (*Y _{i}*) according to the following formula:

where *λ* is the parameter for the transformation. Minitab then creates a control chart of the transformed data values (*W _{i}*). To learn how Minitab chooses the optimal value for

The following table shows some commonly used *λ* values and their transformations.

λ | Transformation |
---|---|

2 | |

0.5 | |

0 | |

−0.5 | |

−1 |