Clinical Chemistry
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Clinical Chemistry 25: 394-400, 1979;
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Clinical Chemistry, Vol 25, 394-400, Copyright © 1979 by American Association for Clinical Chemistry

Influence of a between-run component of variation, choice of control limits, and shape of error distribution on the performance characteristics of rules for internal quality control

JO Westgard, H Falk and T Groth

A computer-stimulation study has been performed to determine how the performance characteristics of quality-control rules are affected by the presence of a between-run component of variation, the choice of control limits (calculated from within-run vs. total standard deviations), and the shape of the error distribution. When a between- run standard deviation (Sb) exists and control limits are calculated from the total standard deviation (St, which includes Sb as well as the within-run standard deviation, Sw), there is generally a loss in ability to detect analytical disturbances or errors. With control limits calculated from Sw, there is generally an increase in the level of false rejections. The presence of non-gaussian error distribution appears to have considerably less effect. It can be recommended that random error be controlled by use of a chi-square or range-control rule, with control limits calculated from Sw. Optimal control of systematic errors is difficult when Sb exists. An effort should be made to reduce Sb, and this will lead to increased ability to detect analytical errors. When Sb is tolerated or accepted as part of the baseline state of operation for the analytical method, then further increases in the number of control observations will be necessary to achieve a given probability for error detection.


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


Home page
 Clin. Chem.Home page
J. O. Westgard and B. Stein
Automated Selection of Statistical Quality-Control Procedures to Assure Meeting Clinical or Analytical Quality Requirements
Clin. Chem., February 1, 1997; 43(2): 400 - 403.
[Full Text] [PDF]

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 Med Decis MakingHome page
R.P. Channing Rodgers
How Much Quality Control is Enough?: A Cost-effectiveness Model for Clinical laboratory Quality Control Procedures (Illustrated by Its Application to a Ligand-assay-based screening Program)
Med Decis Making, August 1, 1987; 7(3): 156 - 167.
[Abstract] [PDF]


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Copyright © 1979 by the American Association for Clinical Chemistry.