Guide to the Expression of Uncertainty in Measurement

Guide to the Expression of Uncertainty in Measurement
Name	Guide to the Expression of Uncertainty in Measurement
Abbrev	GUM
First published	1993
Authors	International Organization for Standardization; Bureau International des Poids et Mesures; International Electrotechnical Commission
Subject	Measurement uncertainty, metrology, statistics
Language	English

Guide to the Expression of Uncertainty in Measurement

The Guide to the Expression of Uncertainty in Measurement is an influential technical document used in metrology, standardization, and measurement science. It provides a framework for quantifying and reporting uncertainty so that results from laboratories, research institutions, and regulatory bodies can be compared and interpreted consistently. The Guide has shaped practice at institutions such as the International Bureau of Weights and Measures, National Institute of Standards and Technology, European Committee for Standardization and national metrology institutes.

Introduction

The Guide was developed through collaboration among the International Organization for Standardization, the International Electrotechnical Commission and the Bureau International des Poids et Mesures to harmonize uncertainty statements used by laboratories like the National Physical Laboratory, Physikalisch-Technische Bundesanstalt, and Laboratoire National de Métrologie et d'Essais. Its genesis involved working groups with contributors from institutions including the American National Standards Institute, the International Laboratory Accreditation Cooperation, and the International Organization of Legal Metrology. The Guide became a reference for accreditation bodies such as the International Laboratory Accreditation Cooperation, national accreditation bodies, and regional metrology organizations.

Principles and Terminology

The Guide defines fundamental terms and principles drawing on statistical concepts used by scientists at the Royal Society, statisticians influenced by Ronald Fisher and Jerzy Neyman, and standards writers from the International Organization for Standardization and the International Electrotechnical Commission. Key terminology includes definitions of standard uncertainty, combined standard uncertainty, and expanded uncertainty, which relate to practice at laboratories like NIST, PTB, and CSIRO. The Guide distinguishes between Type A evaluation based on the Student's t and normal distribution traditions and Type B evaluation informed by authoritative sources such as the International Bureau of Weights and Measures, the World Meteorological Organization, and the International Civil Aviation Organization.

Types and Sources of Uncertainty

The Guide categorizes uncertainties arising from equipment traceability chains exemplified by comparisons among NMIs including the National Research Council, METAS, and KRISS, environmental influences documented by institutions like NASA and ESA, and modeling assumptions used by researchers at CERN, Fermilab, and Brookhaven National Laboratory. Sources include repeatability and reproducibility issues treated in proficiency testing schemes run by organizations like the European Association of National Metrology Institutes, measurement bias related to calibration services from calibration laboratories accredited by ILAC, and uncertainty contributions from physical constants maintained by CODATA and the International Bureau of Weights and Measures.

Evaluation and Quantification Methods

Evaluation methods described in the Guide combine statistical inference rooted in the works of Karl Pearson and William Sealy Gosset with propagation of uncertainty techniques applied by metrologists at INRIM, LNE, and SCL. The Guide prescribes combining variances using the law of propagation of uncertainty, matrix methods used in linear algebra as in publications from the Royal Society, and Monte Carlo methods championed in numerical analysis communities at institutions like the European Centre for Medium-Range Weather Forecasts, Los Alamos National Laboratory, and the University of Cambridge. It references use of coverage factors linked to confidence intervals in the tradition of Neyman and Fisher and computational tools developed at ETH Zurich, Massachusetts Institute of Technology, and Stanford University.

Reporting and Presentation of Results

The Guide prescribes formats for reporting uncertainty to ensure comparability among publications from journals such as Nature, Science, and Metrologia and regulatory reports from bodies like the European Commission, Food and Drug Administration, and International Atomic Energy Agency. It recommends clear statements of measurement result, combined standard uncertainty, and expanded uncertainty using coverage factors and confidence levels familiar to readers of Proceedings of the Royal Society, IEEE Transactions, and Analytical Chemistry. Presentation practices align with reporting requirements of accreditation schemes run by ILAC, ISO/IEC 17025 implementations, and national standards offices such as NIST, PTB, and JIS.

Applications and Examples

The Guide's approaches are applied across domains including time and frequency metrology at observatories like the National Physical Laboratory, chemical analysis in laboratories affiliated with the American Chemical Society, and environmental monitoring programs run by the World Meteorological Organization and United Nations Environment Programme. Examples include calibration of electrical standards at laboratories such as NPL and METAS, spectroscopic measurements in astrophysics research at the European Southern Observatory and Max Planck Institute, and clinical assay validation in hospitals associated with the World Health Organization and Clinical and Laboratory Standards Institute.

Standards and International Guidance

The Guide underpins international standards and guidance such as ISO/IEC 17025, ISO 9001 implementations in testing facilities, and technical recommendations from the International Bureau of Weights and Measures and CODATA. Its principles are echoed in documents produced by the International Organization for Standardization, the International Electrotechnical Commission, the International Laboratory Accreditation Cooperation, and regional metrology organizations like EURAMET and APMP. National metrology institutes including NIST, PTB, NPL, and KRISS incorporate Guide-based methods into calibration certificates, interlaboratory comparisons, and national measurement institutes' calibration and measurement capability statements.

Category:Metrology Category:Standards