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A discussion of some alternative routes of estimating measurement uncertainty for consensus certified reference materials
The certified value of a Certified Reference Material (CRM) must always be accompanied by an estimate of the measurement uncertainty. The internationally accepted way of estimating this uncertainty is given in the ISO publication 'Guide to the Expression of Uncertainty in Measurement' (GUM). However, for reference materials certified by inter-laboratory collaborative studies a number of protocols are currently used world-wide for estimating the uncertainty of certified values. Few of these protocols are so far equivalent to, or compliant with, the GUM. The following discussion paper outlines some of these practices and offers a number of alternative approaches to estimating measurement uncertainty for CRMs certified using the inter-laboratory study approach. Different value assignment calculations are also compared; it is found that while robust estimates and outlier rejection give similar estimates of the certified value, the uncertainty estimates differ significantly.
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