ISO/IEC Guide 98:1993
(Main)Guide to the expression of uncertainty in measurement (GUM)
Guide to the expression of uncertainty in measurement (GUM)
Guide pour l'expression de l'incertitude de mesure (GUM)
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This document provides guidance on developing and using a measurement model and also covers the assessment of the adequacy of a measurement model. The document is of particular interest to developers of measurement procedures, working instructions and documentary standards. The model describes the relationship between the output quantity (the measurand) and the input quantities known to be involved in the measurement. The model is used to obtain a value for the measurand and an associated uncertainty. Measurement models are also used in, for example, design studies, simulation of processes, and in engineering, research and development. This document explains how to accommodate in a measurement model the quantities involved. These quantities relate i) to the phenomenon or phenomena on which the measurement is based, that is, the measurement principle, ii) to effects arising in the specific measurement, and iii) to the interaction with the artefact or sample subject to measurement. The guidance provided is organised in accordance with a work flow that could be contemplated when developing a measurement model from the beginning. This work flow starts with the specification of the measurand (clause 6). Then the measurement principle is modelled (clause 7) and an appropriate form of the model is chosen (clause 8). The basic model thus obtained is extended by identifying (clause 9) and adding (clause 10) effects arising from the measurement and the artefact or sample subject to measurement. Guidance on assessing the adequacy of the resulting measurement model is given in clause 12. The distinction between the basic model and the (complete) measurement model in the work flow should be helpful to those readers who already have a substantial part of the measurement model in place, but would like to verify that it contains all effects arising from the measurement so that it is fit for purpose. Guidance on the assignment of probability distributions to the quantities appearing in the measurement model is given in JCGM 100:2008 and JCGM 101:2008. In clause 11, this guidance is supplemented by describing how statistical models can be developed and used for this purpose. When using a measurement model, numerical problems can arise including computational effects such as rounding and numerical overflow. It is demonstrated how such problems can often be alleviated by expressing a model differently so that it performs well in calculations. It is also shown how a reformulation of the model can sometimes be used to eliminate some correlation effects among the input quantities when such dependencies exist. Examples from a number of metrology disciplines illustrate the guidance provided in this document.
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ISO/IEC Guide 98-4:2012 provides guidance and procedures for assessing the conformity of an item (entity, object or system) with specified requirements. The item might be, for example, a gauge block, a grocery scale or a blood sample. The procedures can be applied where the following conditions exist: the item is distinguished by a single scalar quantity (a measurable property) defined to a level of detail sufficient to be reasonably represented by an essentially unique true value; an interval of permissible values of the property is specified by one or two tolerance limits; the property can be measured and the measurement result expressed in a manner consistent with the principles of the GUM, so that knowledge of the value of the property can be reasonably described by (a) a probability density function, (b) a distribution function, (c) numerical approximations to such functions, or (d) a best estimate, together with a coverage interval and an associated coverage probability. The procedures developed in this document can be used to realize an interval, called an acceptance interval, of permissible measured values of the property of interest. Acceptance limits can be chosen so as to balance the risks associated with accepting non-conforming items (consumer's risk) or rejecting conforming items (producer's risk). Two types of conformity assessment problems are addressed. The first is the setting of acceptance limits that will assure that a desired conformance probability for a single measured item is achieved. The second is the setting of acceptance limits to assure an acceptable level of confidence on average as a number of (nominally identical) items are measured. Guidance is given for their solution. This document contains examples to illustrate the guidance provided. The concepts presented can be extended to more general conformity assessment problems based on measurements of a set of scalar measurands. The audience of this document includes quality managers, members of standards development organizations, accreditation authorities and the staffs of testing and measuring laboratories, inspection bodies, certification bodies, regulatory agencies, academics and researchers.
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ISO/IEC Guide 98-3:2008/Suppl.2:2011 is concerned with measurement models having any number of input quantities and any number of output quantities. The quantities involved might be real or complex. Two approaches are considered for treating such models. The first approach is a generalization of the GUM uncertainty framework. The second is a Monte Carlo method as an implementation of the propagation of distributions. Appropriate use of the Monte Carol method would be expected to provide valid results when the applicability of the GUM uncertainty framework is questionable. For a prescribed coverage probability, ISO/IEC Guide 98-3:2008/Suppl.2:2011 can be used to provide a coverage region for the output quantities of a multivariate model, the counterpart of a coverage interval for a single scalar output quantiy. The provision of coverage regions includes those taking the form of a hyper-ellipsoid or a hyper-rectangle. These coverage regions are produced from the results of the two approaches described here. A procedure for providing an approximation to the smallest coverage region, obtained from results provided by the Monte Carol method, is also given. Detailed examples to illustrate the guidance are provided.
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ISO/IEC Guide 98-1:2009 provides a brief introduction to the “Guide to the expression of uncertainty in measurement” (GUM) in order to indicate the relevance of that fundamental guide and promote its use. It also outlines documents related to the GUM that are intended to extend the application of that guide to broader categories and fields of practical problems. ISO/IEC Guide 98-1:2009 addresses measurement science at a level that is suitable for those readers who have received training at least to the second year of a science- or engineering-based degree course containing some teaching of probability theory and statistics. It also considers various concepts used in measurement science. In particular, it covers the need to characterize the quality of a measurement through appropriate statements of measurement uncertainty. This introductory document also outlines the recent evolution of thinking regarding measurement uncertainty.
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ISO/IEC Guide 98-3/Suppl.1:2008 provides a general numerical approach, consistent with the broad principles of the Guide to the expression of uncertainty in measurement (GUM), for carrying out the calculations required as part of an evaluation of measurement uncertainty. The approach applies to arbitrary models having a single output quantity where the input quantities are characterized by any specified probability density functions (PDFs). ISO/IEC Guide 98-3/Suppl.1:2008 is primarily concerned with the expression of uncertainty in the measurement of a well-defined physical quantity—the measurand—that can be characterized by an essentially unique value. It provides guidance in situations where the conditions for the GUM uncertainty frameworkare not fulfilled, or it is unclear whether they are fulfilled. It can be used when it is difficult to apply the GUM uncertainty framework, because of the complexity of the model, for example. Guidance is given in a form suitable for computer implementation. ISO/IEC Guide 98-3/Suppl.1:2008 can be used to provide (a representation of) the PDF for the output quantity from which (a) an estimate of the output quantity, (b) the standard uncertainty associated with this estimate, and (c) a coverage interval for that quantity, corresponding to a specified coverage probability, can be obtained. For a prescribed coverage probability, it can be used to provide any required coverage interval, including the probabilistically symmetric coverage interval and the shortest coverage interval. ISO/IEC Guide 98-3/Suppl.1:2008 applies to input quantities that are independent, where each such quantity is assigned an appropriate PDF, or not independent, i.e. when some or all of these quantities are assigned a joint PDF. Detailed examples illustrate the guidance provided.
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ISO/IEC Guide 98-3:2008 is a reissue of the 1995 version of the Guide to the Expression of Uncertainty in Measurement (GUM), with minor corrections. This Guide establishes general rules for evaluating and expressing uncertainty in measurement that can be followed at various levels of accuracy and in many fields — from the shop floor to fundamental research. The principles of this Guide are intended to be applicable to a broad spectrum of measurements, including those required for: maintaining quality control and quality assurance in production; complying with and enforcing laws and regulations; conducting basic research, and applied research and development, in science and engineering; calibrating standards and instruments and performing tests throughout a national measurement system in order to achieve traceability to national standards; developing, maintaining, and comparing international and national physical reference standards, including reference materials.
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ISO/IEC Guide 99:2007 provides a set of definitions and associated terms, in English and French, for a system of basic and general concepts used in metrology, together with concept diagrams to demonstrate their relations. Additional information is given in the form of examples and notes under many definitions. This Vocabulary is meant to be a common reference for scientists and engineers, as well as teachers and practitioners, involved in planning or performing measurements, irrespective of the level of measurement uncertainty and irrespective of the field of application. It is also meant to be a reference for governmental and inter-governmental bodies, trade associations, accreditation bodies, regulators and professional societies.
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This document — introduces conditions, constraints and resources necessary to evaluate a measurement method or a result; — defines an organizational scheme for the acquisition of trueness and precision data by study; — provides the necessary definitions, statistical model and principles for ISO 5725 (all parts). — is not applicable to proficiency testing or production of the reference item that has their own standards (ISO 13528, respectively and ISO Guide 35). This document is concerned exclusively with measurement methods which yield results on a continuous scale and give a single value as the test result, although this single value may be the outcome of a calculation from a set of observations. It defines values which describe, in quantitative terms, the ability of a measurement method to give a true result (trueness) or to replicate a given result (precision). Thus, there is an implication that exactly the identical item is being measured, in exactly the same way, and that the measurement process is under control. This document may be applied to a very wide range of test items, including gas, liquids, powders and solid objects, manufactured or naturally occurring, provided that due consideration is given to any heterogeneity of the test item. This document does not include methods of calculation that are described in the other parts.
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- 19-Jul-2023
- 03.120.30
- 17.020
- ISO/TC 69/SC 6
This document provides a) a discussion of alternative experimental designs for the determination of trueness and precision measures including reproducibility, repeatability and selected measures of intermediate precision of a standard measurement method, including a review of the circumstances in which their use is necessary or beneficial, and guidance as to the interpretation and application of the resulting estimates, and b) worked examples including specific designs and computations. Each of the alternative designs discussed in this document is intended to address one (or several) of the following issues: a) a discussion of the implications of the definitions of intermediate precision measures; b) a guidance on the interpretation and application of the estimates of intermediate precision measures in practical situations; c) determining reproducibility, repeatability and selected measures of intermediate precision; d) improved determination of reproducibility and other measures of precision; e) improving the estimate of the sample mean; f) determining the range of in-house repeatability standard deviations; g) determining other precision components such as operator variability; h) determining the level of reliability of precision estimates; i) reducing the minimum number of participating laboratories by optimizing the reliability of precision estimates; j) avoiding distorted estimations of repeatability (split-level designs); k) avoiding distorted estimations of reproducibility (taking the heterogeneity of the material into consideration). Often, the performance of the method whose precision is being evaluated in a collaborative study will have previously been assessed in a single-laboratory validation study conducted by the laboratory which developed it. Relevant factors for the determination of intermediary precision will have been identified in this prior single-laboratory study.
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- 27-Jun-2023
- 03.120.30
- 17.020
- ISO/TC 69/SC 6
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