Proficiency testing and interlaboratory comparisons
Laboratories demonstrate that their results are consistent with others by measuring the same artefact. The En number tells whether a result agrees within its uncertainty.
Uncertainty budgets are models; comparisons are the experiment that tests them. In an interlaboratory comparison a stable artefact — a reference PRT, a set of loggers — is circulated and each laboratory reports its value and uncertainty. The results are compared with a reference value, usually from a pilot laboratory or an NMI.
Interpreting E_n
- |E_n| ≤ 1: the difference from the reference is within the combined expanded uncertainties — consistent.
- |E_n| > 1: inconsistent; investigate the measurement or the uncertainty claim.
- |E_n| ≪ 1 for all points: possibly an over-estimated uncertainty.
For customers, asking whether a laboratory participates in comparisons for the quantity you need is a reasonable due-diligence question.
Frequently asked questions
- Is proficiency testing mandatory for accreditation?
- Accreditation bodies require participation according to their policies where schemes are available; the laboratory plans participation across its scope over a cycle.
References
- [1]ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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