2. Main references for uncertainty evaluation

In order to harmonize the uncertainty evaluation process for every laboratory, the Bureau International des Poids et Mesures (BIPM) published in 1980 the Recommendation INC-1 [2] on how to express uncertainty in measurement. This document was further developed and originated the "Guide to the Expression of Uncertainty in Measurement"—GUM in 1993, which was revised in 1995 and lastly in 2008. This document provides complete guidance and references on how to treat common situations on metrology and how to deal with uncertainties in metrology. Currently, it is published by International Organization for Standardization (ISO) as the ISO/IEC Guide 98-3 "Uncertainty of measurement—Part 3: Guide to the expression of uncertainty in measurement" (GUM), and by the Joint Committee for Guides in Metrology (JCGM) as the JCGM 100:2008 guide [3]. The JCGM was established by BIPM to maintain and further develop the GUM. They are in fact currently producing a series of documents and supplements to accompany the GUM, four of which are already published [4–7].

Evaluation of uncertainty, as presented by the JCGM 100:2008, is based on the law of propagation of uncertainties (LPU). This methodology has been successfully applied for several years worldwide for a range of different measurement systems and is currently the most used procedure for uncertainty evaluation in metrology. However, since its twentieth anniversary in 2013, JCGM decided to revise it again [8–10]. In this new revision, uncertainty terms and concepts [11] will be aligned with the current International Vocabulary of Metrology (VIM) [12] and with the new GUM supplements [5, 6]. Aspects such as a new Bayesian approach, the redefinition of coverage intervals and the elimination of the Welch-Satterthwaite formula to evaluate the effective degrees of freedom will be covered [9]. In late 2014, a first draft of the newly revised version of the GUM was circulated among National Metrology Institutes. Remarkable changes were made that could affect the way laboratories deal with the measurement uncertainty results. This revision is still being discussed, and some information about it has also been released elsewhere [10].

In the field of analytical chemistry, there is also another document worth mentioning that is the "Quantifying Uncertainty in Analytical Measurement" guide [13], produced by a joint EURACHEM/CITAC Measurement Uncertainty Working Group. This document was first published in 1995 and further revised in 2000 [14]. This last edition had a widespread implementation and is among the most highly cited publications in chemical metrology area [14]. Recently, a new revised edition was published in 2012 with improved content and added information on developments in uncertainty evaluation [14]. This document basically presents the uncertainty evaluation process following the suggestions of the GUM, but also contains several examples in the analytical chemistry area.
