DS/ISO/IEC Guide 98-4:2012

Uncertainty of measurement - Part 4: Role of measurement uncertainty in conformity assessment

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This document 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 [3.2.1], or characteristic, defined to a level of detail suficient to be reasonably represented by an essentially unique true value;
- an interval of permissible true values of the characteristic is specified by one or two tolerance limits;
- the characteristic can be measured and the measurement result [3.2.5] expressed in a manner consistent with the principles of the GUM, so that
- knowledge of the true value of the characteristic can be reasonably described by (a) a probability density function (PDF), (b) a distribution function [3.1.1], (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 characteristic. 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 characteristics.
The audience of this document includes quality managers, members of standards development organizations, accreditation authorities and the staffs of testing laboratories, inspection bodies, certification bodies and regulatory agencies.

Number of pages: 68

Published: 2012-12-13

Date of approval: 2012-12-12

International relationships : ISO/IEC Guide 98-4:2012 IDT

ICS: 17.020 - Metrology and measurement in general

Item number: M244391