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Clinical Chemistry 39: 1638-1649, 1993;
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Clinical Chemistry, Vol 39, 1638-1649, Copyright © 1993 by American Association for Clinical Chemistry

Comparison of quality-control rules used in clinical chemistry laboratories

J Bishop and AB Nix
School of Mathematics, University of Wales College of Cardiff, UK.

Numerous papers have been written to show which combinations of Shewhart-type quality-control charts are optimal for detecting systematic shifts in the mean response of a process, increases in the random error of a process, and linear drift effects in the mean response across the assay batch. One paper by Westgard et al. (Clin Chem 1977;23:1857-67) especially seems to have attracted the attention of users. Here we derive detailed results that enable the characteristics of the various Shewhart-type control schemes, including the multirule scheme (Clin Chem 1981;27:493-501), to be calculated and show that a fundamental formula proposed by Westgard et al. in the earlier paper is in error, although their derived results are not seriously wrong. We also show that, from a practical point of view, a suitably chosen Cusum scheme is near optimal for all the types and combinations of errors discussed, thereby removing the selection problem for the user.


The following articles in journals at HighWire Press have cited this article:


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 Clin. Chem.Home page
C. A. Parvin and A. M. Gronowski
Effect of analytical run length on quality-control (QC) performance and the QC planning process
Clin. Chem., November 1, 1997; 43(11): 2149 - 2154.
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Copyright © 1993 by the American Association for Clinical Chemistry.