ILAC has recently published a revision of the key guidance document on decision rules and statements of conformity.

To reflect the renewed inportance of decision rules in ISO 17025:2017, the title of the new ILAC G8 has been changed from "Guidelines on the Reporting of Compliance with Specification" to "Guidelines on Decision Rules and Statements of Conformity In ISO/IEC 17025". The revised guidance can be found on the ILAC website.

Overview

The revised ISO/IEC 17025:2017 recognizes that no single decision rule can address all statements of conformity across the diverse scope of testing and calibration. ILAC G8:2019 provides an overview for assessors, laboratories, regulators and customers concerning decision rules and conformity with requirements. It does not enter into the details regarding underlying statistics and mathematics but refers readers to the relevant literature.

This new revision provides:

1. overall guidance on how to select appropriate decision rules; and
2. guidance on compiling the required elements of a decision rule if no standard published rules apply.

Contents

The new ILAC G8 includes useful definitions related to conformity assessment and specification; a reminder of the requirements of ISO 17025:2017; and a general introduction to ideas of measurement uncertainty and decision risk. Like JCGM and Eurachem documents on the topic [1,2], the guidance includes a description of "guard bands" as one important strategy for taking account of measurement uncertainty in decisions on conformity; another is the direct use of measurement uncertainty information.

For more mathematical treatment, the document refers to JCGM 106:2012, Evaluation of measurement data – The role of measurement uncertainty in conformity assessment. [1] In the JCGM document from 2012 two different decision rules are presented:

1. Decision rules based on simple acceptance (shared risk) (section 8.2) and
2. Decision rules based on guard bands (section 8.3).

In the ILAC G8 2009 document the main decision rule presented was using guard bands and in the revised ILAC G8 2019 both decision rules are more clearly described.  

In addition to the general discussion, the new guide includes a useful decision flowchart to aid in teh selection of the most appropriate choice of decision rule.

Further reading

1. JCGM 106:2012, Evaluation of measurement data – The role of measurement uncertainty in conformity assessment. Available from https://www.bipm.org/en/publications/guides/

2. S L R Ellison and A Williams (Eds). Eurachem/CITAC guide: Use of uncertainty information in compliance assessment. (First Edition) (2007).  www.eurachem.org

3. Eurachem Information Leaflet Use of uncertainty information in compliance assessment (2009)

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Published: Monday, 14 October 2019 23:58

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