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South African Journal of Industrial Engineering

On-line version ISSN 2224-7890
Print version ISSN 1012-277X


CHIN, W.S.  and  KHOO, M.B.C.. A study of the median run length (MRL) performance of the EWMA t chart for the mean. S. Afr. J. Ind. Eng. [online]. 2012, vol.23, n.3, pp.42-55. ISSN 2224-7890.

The exponentially weighted moving average (EWMA) X chart is effective in detecting small shifts. However, the EWMA X chart is not robust enough to prevent errors in estimating the process standard deviation or a changing standard deviation. To overcome this problem, Zhang et al. suggested the EWMA t chart in 2009. The existing optimal design of the EWMA t chart is based on the average run length (ARL) criterion. This paper proposes that the optimal design of the EWMA t chart be based on the median run length (MRL). The MRL performances of the optimal EWMA X and optimal EWMA t charts are compared.

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