A double sampling multivariate T2 control chart with variable sample size and variable sampling interval

This paper presents an adaptive T-2 control chart for monitoring shifts in the mean vector of a multivariate normally distributed process. This chart which combines the double sampling, variable sample size and variable sampling interval features, called the DSVSSI T-2 chart and uses three different sample sizes, two different sampling intervals, two warning limits and two different control limits. A Markov chain approach is employed to compute the statistical performance measures. The proposed chart is compared with the existing standard T-2 and other adaptive multivariate T-2 charts. In all cases, the DSVSSI T-2 chart is quicker at detecting small to moderate shifts in the mean vector. An example is provided to illustrate the construction and implementation of the DSVSSI T-2 chart. Finally, some concluding remarks are given.