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Addressing Measurement Uncertainty
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 November 2005 Letter to the Editor

Addressing Measurement Uncertainty

I read with interest the article by Neil Ullman in the October 2005 issue of the SN that addresses measurement uncertainty. I am a member of Subcommittee E10.01 on Dosimetry in Radiation Processing, which has jurisdiction over ISO/ASTM 51707, Guide for Estimating Uncertainties in Dosimetry for Radiation Processing. This standard, which was first published in 1995, incorporated the Guide to the Expression of Uncertainty in Measurements (GUM) approach in the methodology for measurement uncertainty. The latest revision of this standard also follows this approach for estimating uncertainty in dosimetry measurements. Measurement uncertainty in dosimetry applies to the results of a single measurement that depends on a specific measurement configuration, i.e., we are not dealing with a test method. The GUM approach provides a quantitative method for estimating uncertainty in dosimetry for radiation processing.

The article by Dr. Ullman aptly differentiates between the metrologist’s “measurement methods” and ASTM “test methods.” However, the revision of section A22 of Form and Style for ASTM Standards does not provide that differentiation. It was the recommendation of Committee E10 on Nuclear Technology and Applications in 2004, at the suggestion of Subcommittee E10.01, that section A22 be titled “ASTM Guidance on Measurement Uncertainty in Test Methods.” It was believed that the additional words would have helped to denote the difference between the metrologist’s “measurement methods” and ASTM “test methods.” It should be noted that many of the ASTM standards that have been developed by Subcommittee E10.01 are now ISO/ASTM standards and the GUM approach for estimating uncertainty in dosimetry for radiation processing has proven to be a viable method for comparing dosimetry measurements from around the world.

Barry P. Fairand,
Member Subcommittee E10.01
Senior Consultant
Sterigenics International, Inc.

Author’s Response

Mr. Fairand raises some interesting issues. I cannot speak for the ASTM Committee on Standards, but my understanding is that section A of Form and Style for ASTM Standards is strictly the “Form of ASTM Test Methods.” So the section now listed as A22 deals only with test methods, as does section A21 on Precision and Bias.

Apparently all of the E10 standards for which the “Standard Guide for Estimating Uncertainties in Dosimetry for Radiation Processing” applies are guides or practices and neither of those would be addressed by section A22.

I do find it fascinating that even though these E10 standards are not test methods, and are not subjected to interlaboratory programs to determine precision (repeatability and reproducibility), individual laboratory results are being compared worldwide by just determining laboratory uncertainties.

—Neil Ullman

 
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