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Articles |
Institut für Klinische Chemie und Pathobiochemie (Director: Prof. D. Neumeier), Klinikum rechts der Isar der Technischen Universität München, Ismaninger Str. 22, 81675 Munich, Germany. Fax 89-4140 4875; e-mail A.S.Neubauer{at}lrz.tu-muenchen.de
A quality-control chart based on exponentially weighted moving averages (EWMA) has, in the past few years, become a popular tool for controlling inaccuracy in industrial quality control. In this paper, I explain the principles of this technique, present some numerical examples, and by computer simulation compare EWMA with other control charts currently used in clinical chemistry. The EWMA chart offers a flexible instrument for visualizing imprecision and inaccuracy and is a good alternative to other charts for detecting inaccuracy, especially where small shifts are of interest. Detection of imprecision with EWMA charts, however, requires special modification.
Key Words: indexing terms: statistics exponentially weighted moving average Shewhart chart, Westgard algorithm compared
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