This guide has been produced by a joint EURACHEM/CITAC Measurement Uncertainty Working Group in collaboration with representatives from AOAC International, IAEA, and EA. Production of the guide was in part supported under the contract with the UK Department of Trade and Industry as part of the National Measurement System Valid Analytical Measurement (VAM) Programme.
The first version of this guide, which was published in 1995, has been very well received. It has been very widely used and two successful workshops on its utilisation have been held since its publication. Following from these workshops and the many helpful comments the working group has received on the contents of the first edition, many significant changes and improvements have been made in this second edition. The most important change deals with the use of method performance data and in particular the use of method validation data, from both collaborative validation studies and from in-house studies. The new sections dealing with the use of method performance data show that in many cases such data gives all, or nearly all information required to evaluate the uncertainty. The format of the guide is very similar to that of the first edition with chapters 1 and 2 dealing with the scope and the concept of uncertainty as before. Chapter 3, Analytical Measurement and Uncertainty, is completely new and covers the process of method validation and conduct of experimental studies to determine method performance and their relationship to uncertainty estimation. There is also a new section on traceability. The chapter on uncertainty estimation in the previous guide has been considerably expanded and split into four separate chapters, dealing with the four steps involved in estimating uncertainty. Step 1 deals with the specification of the measurand, Step 2 with identifying the uncertainty sources, Step 3, which has been considerably expanded to cover the use of existing method validation data, deals with quantifying the uncertainty and Step 4 covers the calculation of the combined uncertainty. The examples have been completely revised and new ones added. They are now all in a standard format, which follow the four steps described above. They all utilise the cause and effect diagram as an aid to identifying the sources of uncertainty and to ensuring that all the significant ones are included in the evaluation of the uncertainty.
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