A special variable sample size and sampling interval Hotelling’s T2 chart

Among the variable sampling interval (VSI), variable sample size (VSS), and variable sample size and sampling interval (VSSI) T2 charts that use two values of each adaptive parameter, a VSI T2 chart is the most efficient chart to detect large shifts in the process mean vector while a VSSI T2 chart is the most efficient one to detect small shifts. The statistical performance of the T2 chart proposed in this paper very closely matches that of such VSI and VSSI T2 charts for detecting the large and small shifts, respectively. The proposed chart uses two values of the sampling interval and three values of the sample size.