Quantify uncertainty and repeatability

What the unit asks

The draft makes the point that without a quantitative view of uncertainty it is impossible to tell whether a difference between two systems is real or is experimental noise. That matters most when the two systems are close, which is exactly the case in a shortlist. Repeatability and reproducibility are different claims and should be labelled separately.

What good practice looks like

Report the interval, not only the point estimate. Keep the repeat run and its conditions. Where a second laboratory is used, report its result and the conditions that changed. Do not treat a difference inside the interval as a ranking.

Evidence an assessor asks for

What a good answer sounds like

A good answer to P3-13 names The uncertainty statement for each headline figure., dates it, and says what it does not cover. A policy or a promise is not an answer. If P3-13 has no artefact, the row is not met and the absence is the finding.

Where comparisons commonly fail

• Two systems are ranked on a difference smaller than the interval.
• The repeat run is done on a different sample and compared as if it were the same.
• No uncertainty is reported because the figure is a percentage.

Questions to put to the supplier

1. Is the gap between these systems larger than the uncertainty?
2. Would a second laboratory get the same result?

How this is used in the kit

P3-13 becomes one row of the comparison register, with an owner, a status and the evidence named above. A status of met asks for the artefact and its date, and the free check uses the same row as an evidence question, so the page and the register share one vocabulary.