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Specialized Control Charts |

See SHWT2 in the SAS/QC Sample Library |

In many industrial applications,
the output of a process
characterized by *p* variables that are measured simultaneously.
Independent variables can be charted individually, but if the
variables are correlated, a multivariate chart is needed to
determine whether the process is in control.

Many types of multivariate control charts have been
proposed; refer to Alt (1985) for an overview.
Denote the *i*^{ th} measurement on the
*j*^{ th} variable as
*X*_{ij} for *i* = 1,2, ... ,*n*, where *n* is the number of
measurements, and *j* = 1,2, ... ,*p*.
Standard practice is to construct a chart for a statistic
*T ^{2}*

and

In this example, a multivariate control chart is
constructed using a beta distribution for *T ^{2}*

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