- Volume 23 Issue 4
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Multivariate EWMA control charts for monitoring the variance-covariance matrix
- Jeong, Jeong-Im (Department of Statistics, Kyungpook National University) ;
- Cho, Gyo-Young (Department of Statistics, Kyungpook National University)
- Received : 2012.05.14
- Accepted : 2012.06.05
- Published : 2012.07.31
We know that the exponentially weighted moving average (EWMA) control charts are sensitive to detecting relatively small shifts. Multivariate EWMA control charts are considered for monitoring of variance-covariance matrix when the distribution of process variables is multivariate normal. The performances of the proposed EWMA control charts are evaluated in term of average run length (ARL). The performance is investigated in three types of shifts in the variance-covariance matrix, that is, the variances, covariances, and variances and covariances are changed respectively. Numerical results show that all multivariate EWMA control charts considered in this paper are effective in detecting several kinds of shifts in the variance-covariance matrix.
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