These functions are used to compute statistics required by the *T^2* chart.

1 2 3 |

`data` |
the observed data values |

`center` |
a vector of values to use for center of input variables. |

`cov` |
a matrix of values to use for the covariance matrix of input variables. |

`ngroups` |
number of groups |

`size` |
sample size |

`nvars` |
number of variables |

`conf` |
confidence level (0 < |

The function `stats.T2`

returns a list with components:

`statistics` |
a vector of values for the |

`means` |
a matrix of within group means for each variable |

`center` |
sample/group center statistic |

`S` |
covariance matrix |

The function `limits.T2`

returns a list with components:

`control` |
control limits |

`prediction` |
pred.limits |

Luca Scrucca luca@stat.unipg.it

Mason, R.L. and Young, J.C. (2002) *Multivariate Statistical Process Control with Industrial Applications*, SIAM.

Montgomery, D.C. (2005) *Introduction to Statistical Quality Control*, 5th ed. New York: John Wiley & Sons.

Ryan, T. P. (2000), *Statistical Methods for Quality Improvement*, 2nd ed. New York: John Wiley & Sons, Inc.

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