Chin, W.S. and Khoo, M.B.C.
(2012)
A study of the median run length (MRL) performance of the EWMA t chart for the mean.
South African Journal of Industrial Engineering, 23 (3).
pp. 42-55.
ISSN 1012-277X
Abstract
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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