VARIABLE SAMPLE SIZE AND SAMPLING INTERVALS WITH FIXED TIMES HOTELLING'S T2 CHART

The idea of variable sample size and variable sampling interval with sampling at fixed times is extended to the Hotellling's T-2 chart in this study. This chart is called variable sample size and sampling intervals with fixed times (VSSIFT) Hotellling's T-2 chart, in which samples with sample size n always be taken at some specified fixed equally spaced time points but additional samples larger than n are allowed between these time points whenever there is some indication of a process mean shift. The numerical comparison shows that the VSSIFT Hotellling's T-2 chart and the variable sampling interval and variable sample size (VSSI) Hotellling's T-2 chart give almost the same effectiveness in detecting shifts in the process mean. However, from the administration viewpoint, the VSSIFT chart is considered to be more convenient than the VSSI chart.