A variable sampling interval S²-EWMA control chart for monitoring the process variance
by P. Castagliola, G. Celano, S. Fichera, F. Giuffrida
International Journal of Technology Management (IJTM), Vol. 37, No. 1/2, 2007

Abstract: This paper proposes a Variable Sampling Interval version of the Fixed Sampling Interval S²-EWMA control chart developed by Castagliola (2004) and dedicated to the monitoring of the sample variance of a process. In this paper, we explain how the various parameters of this VSI S²-EWMA control chart can be computed and how the use of the VSI feature significantly improves the statistical efficiency of FSI S²-EWMA chart, thus representing an effective tool in the detection of process out-of-control conditions. An optimal design strategy based on the Average Time to Signal (ATS) is presented and a comparison with the FSI procedure is performed.

Online publication date: Sat, 23-Dec-2006

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