Dictionary · Quality & Accreditation
Test accuracy ratio (TAR)
The legacy ratio of unit-under-test tolerance to the accuracy specification of the standard used. Superseded in rigorous work by the test uncertainty ratio, which accounts for the whole measurement process.
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Proficiency testing
Evaluation of participant performance against pre-established criteria by means of interlaboratory comparisons — an ISO/IEC 17025 requirement for demonstrating ongoing competence.
ISO/IEC 17043:2023
Test uncertainty ratio (TUR)
The ratio of the tolerance of the unit under test to the expanded uncertainty of the measurement process used to test it. A 4:1 TUR is the traditional benchmark; lower ratios call for guard banding or risk analysis (ANSI/NCSL Z540.3).
ANSI/NCSL Z540.3
Accreditation
Third-party attestation, by an authoritative body, of a conformity assessment body's competence to carry out specific tasks — for laboratories, against ISO/IEC 17025, by bodies operating under ISO/IEC 17011.
ISO/IEC 17011:2017
Interlaboratory comparison
Organization, performance, and evaluation of measurements on the same or similar items by two or more laboratories under predetermined conditions.
ISO/IEC 17043:2023
Guard band
An interval applied between the tolerance limit and the acceptance limit to control the risk of false accept or false reject given measurement uncertainty — commonly the expanded uncertainty U, per ILAC-G8.
ILAC-G8:09/2019
Decision rule
A documented rule describing how measurement uncertainty is accounted for when stating conformity with a specified requirement — required by ISO/IEC 17025:2017 when a laboratory reports pass/fail.
ISO/IEC 17025:2017, 3.7