Some quality control schemes have been developed when several related
quality characteristics are to be monitored: simultaneous (X) over bar
charts, Hotelling's T-2 chart, multivariate CUSUM and multivariate EW
MA. Hotelling's T-2 control chart has the advantage of its simplicity
but it is slow in detecting small process shifts. The latest developme
nts in variable sample sizes for univariate control charts are applied
in this paper to define an adaptive sample sizes T-2 control chart. A
s occurs in the univariate case the ARL improvements are very importan
t particularly for small process shifts. An example is given to illust
rate the use of the proposed scheme.