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5.3 Standard Reference Materials

Carroll Croarkin, Lisa Gill, Mark Vangel, Mark Levenson
Statistical Engineering Division, ITL

The Statistical Engineering Division supports the Standard Reference Materials Program and the other NIST laboratories by collaborating directly with chemists and other scientists engaged in the certification of Standard Reference Materials (SRMs). SRMs are artifacts or chemical compositions that are manufactured according to strict specifications and certified by NIST for one or more quantities of interest. SRMs are a primary vehicle for disseminating measurement technology to industry.

Development of a new SRM typically takes about five years and encompasses: 1) validation of a measurement method; 2) design of a prototype; 3) stability testing; 4) study of measurement error; 5) certification uncertainty analysis. Statisticians advise on the design and analysis of experiments at all phases; develop estimation methods for data from different analytical methods; help reconcile interlaboratory differences; and combine all information to produce a certified value and statement of uncertainty.

Over the years, statements of uncertainty, as they appear on SRM certificates, have been more diverse than uniform, and this creates a problem both for the user community and the Office of Standard Reference Materials. Therefore, SED is striving to develop and adopt two or three coherent, uniform methods for reporting uncertainties. Lisa Gill, Mark Vangel, and Mark Levenson have taken the lead in raising the pertinent issues and providing recommendations for the future in a forum established for this purpose within the division.

In 1998, approximately twenty-five new SRMs were assigned to division staff; fifty SRM certifications were completed; and fifty SRMs are still in some phase of development. Tracking the number and status of SRMs has always been challenging because the responsibility for the status of the certification process often shifts back and forth between scientist and statistician as follow-on data are taken and analyzed or more analytes are added to the certification process.

The largest number of SRMs, far and away, came from the Chemical Science Technology Laboratory (CSTL), but SRMs from the other NIST laboratories covered a variety of applications, for example: Manufacturing Engineering Laboratory (e.g. sinusoidal roughness); Material Science Engineering Laboratory (e.g. Knoop hardness); Electronics and Electrical Engineering Laboratory (e.g. resistivity of silicon wafers); Physics Laboratory (e.g. optical density filters); Building and Fire Research Laboratory (e.g. thermal resistance of fibrous glass insulation).

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Date created: 7/20/2001
Last updated: 7/20/2001
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