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Clinical Chemistry 52: 1204-1205, 2006; 10.1373/clinchem.2006.069591
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(Clinical Chemistry. 2006;52:1204-1205.)
© 2006 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Uncertainty Intervals Based on Deleting Data Are Not Useful

Jan S. Krouwer

1 Krouwer Consulting, 26 Parks Drive, Sherborn, MA 01770, Fax 508-647-9380, E-mail jan.krouwer{at}comcast.net


To the Editor:

Dimech et al. (1) point out that uncertainty intervals are required for assays by many regulatory agencies, and the authors provide a method for calculating uncertainty intervals for serologic assays. Krouwer (2) has critiqued the use of uncertainty intervals based on GUM (Guide to the Expression of Uncertainty in Measurement) for commercial diagnostic assays. The method proposed by Dimech et al. (1) is based on the EURACHEM/CITAC guide (3), which is itself based on GUM.

One of the first steps in the Dimech method is to delete outliers. It is hard to imagine why an uncertainty interval should not include all data and what such an uncertainty interval means when it is not based on all of the data. Maybe the authors assume that outliers are caused by blunders and that they wish to limit their uncertainty interval to the analytical process. Perhaps, but one cannot know that this assumption is true. Moreover, in the EURACHEM/CITAC guide, there is a specific example in which an outlier is deleted because of an analytical root-cause error (an instrumentation problem).

By use of nonparametric methods based on empirical distributions, uncertainty intervals can be estimated without deleting data (4). If these intervals are too large, one should try to discover root causes, not delete data.


References

  1. Dimech W, Francis B, Kox J, Roberts G. Calculating uncertainty of measurement for serology assays by use of precision and bias. Clin Chem 2006;52:526-529.[Abstract/Free Full Text]
  2. Krouwer JS. A critique of the GUM method of estimating and reporting uncertainty in diagnostic assays. Clin Chem 2003;49:1818-1821.[Abstract/Free Full Text]
  3. Eurachem/CITAC. Quantifying uncertainty in analytical measurement, available at http://www.measurementuncertainty.org/mu/QUAM2000-1.pdf (accessed March 1, 2006)..
  4. . Clinical and Laboratory Standards Institute. Estimation of total analytical error for clinical laboratory methods; approved guideline. CLSI document EP21-A 2003 CLSI Wayne, PA. .




This Article
Right arrow Extract Freely available
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the Editor about this paper
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PubMed
Right arrow PubMed Citation
Right arrow Articles by Krouwer, J. S.
Related Collections
Right arrow Laboratory Management
Right arrow Informatics and Statistics

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