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Model Evaluation Under Regulation.

Article 15 obliges a provider to state the accuracy levels of a high-risk system and the metrics behind them. Annex IV obliges the technical file to describe how those levels were established.

Neither says which metric, measured on which population, against which threshold, or judged by whom. The harmonised standard written to settle that, prEN 18229-2, was at draft stage at CEN-CENELEC JTC 21 as of the most recent public information.

So a provider shipping in 2027 makes three choices nobody has ratified, and defends them later against a document that did not exist when the choices were made.

In depth

The Duty Names A Number And Leaves The Method To You.

01

An accuracy figure travels and its conditions do not.

It starts in a slide, moves to a datasheet, reaches the instructions for use, and by the third hop it is a bare percentage. The conditions are the claim: which task definition, which population the items were drawn from, what counted as correct, how refusals and ties were scored, and the confidence interval at that sample size. Two providers can publish the same number for systems that differ widely in the only use anybody cares about.

In shortTwo providers can publish the same number for system…
02

Reported agreement is the flattering statistic, and the gap is large.

Across a nine-provider panel of judge models, the margin by which exact-match agreement overstated Cohen's kappa on MT-Bench averaged 38.6 points and never fell below 33.8 (Norman, Rivera and Hughes, UC Berkeley School of Information, 2026). A judge presented as 85% in agreement therefore sits at a kappa near 0.48, which is moderate. A declaration built on the first statistic and audited against the second does not survive the meeting.

In shortA declaration built on the first statistic and audit…
03

The evaluation set is kept like fixture code.

Items accumulate: one written by an engineer in week two, one lifted from a public benchmark, one taken from a customer ticket nobody screened for personal data, and a growing share generated by the model's own family. Article 10 reaches straight into that file and asks whether the test population resembles the deployment population, which only per item provenance can answer. Provenance is captured when an item is admitted or it is gone, and no amount of later effort reconstructs it from a file of strings.

In shortProvenance is captured when an item is admitted or i…
04

The threshold is usually a round number with no author.

Somebody wrote 95% into a quality gate eighteen months ago, and the honest reason is that it looked right and the suite passed. Article 9 treats residual risk as a judgement against the intended purpose, which makes the threshold a risk decision rather than an engineering preference, and the one part of the apparatus a regulator can assess with no measurement standard in force. Write down the harm, the costlier failure direction, the fallback when the gate is not met, the signatory and the review date.

In shortthe signatory and the review date
The detail

Three Obligations That Land On The Measurement System Itself.

Seven obligations in the paper are restated as demands on the measurement apparatus rather than on the system as a whole. These three are what a notified body or an enterprise auditor asks for first, and none of them can be produced after the fact.

Zone · 01

The metric definition sheet

Article 15 wants a level and its relevant metrics in the instructions for use, which means a formula, the scoring rules for ties and refusals, the eval set version, the sample size and the interval around the figure. Where a judge produced the number, state kappa and say so. Dated and owned, or it is a percentage.

Zone · 02

Per item provenance

Article 10 asks that testing sets be relevant, representative and examined for bias against the setting the system will be used in. That is answerable only item by item: where it came from, who approved it, which deployment segment it stands for, and whether anyone checked it against the training corpus. Record it at admission.

Zone · 03

The versioned evaluation history

Substantial modification turns on being able to say which change moved which number and by how much. Pin the eval set version, the rubric version, the judge version and its validation to every figure you declare, with a date. Releases then produce deltas you can show, instead of an assertion that nothing material happened.

By the numbers

The figures that make it a board-level conversation.

DRAFT
the status of prEN 18229-2 at CEN-CENELEC JTC 21, the measurement standard written for Article 15
38.6 pp
average gap between exact-match agreement and Cohen's kappa across 21 judge models
2 Dec 2027
when Annex III stand-alone high-risk duties fall due, declaration and technical file included
Inside the report

What you'll take away.

01

Step 1 - Declare the metric with its measurement conditions attached

Formula, scoring rules, eval set version, sample size and interval travel with the figure into the instructions for use. Where a judge produced it, report kappa and name the statistic you used.

02

Step 2 - Capture provenance at the moment an item is admitted

Source, approver, deployment segment and a contamination check against the training corpus, recorded per item. This is the single artefact in the file that no later effort can recreate at any price.

03

Step 3 - Give the threshold an author, a harm and a review date

Name what a failure costs the person at the other end, which failure direction is worse, what the fallback does when the gate fails, and who signed. That part is assessable today.

04

Step 4 - Write every methodological choice down as a choice

Why this metric for this harm, why this population, why this threshold, why this judge and what validated it. A recorded rationale maps onto a standard the week one is cited.

Questions

Frequently asked.

The standards are still drafts. Does that let us wait?

No. Article 15 binds whether or not a method has been ratified, and the declaration is due at conformity assessment. prEN 18229-2 and the related JTC 21 drafts were at draft stage as of the most recent public information, and a standard confers a presumption of conformity only once the Commission cites it in the Official Journal.

Which drafts should we be tracking at CEN-CENELEC JTC 21?

prEN 18229-2 for accuracy, prEN ISO/IEC 23282 for natural language processing evaluation methods, prEN 18281 for computer vision and prEN 18286 for the AI quality management system. All were at draft stage as of the most recent public information, and status moves, so check it rather than quoting this page in a year.

We report our judge at 85% agreement with human raters. Is that enough?

It is the flattering statistic. Berkeley's cohort of 21 judge models across roughly 541,000 judgments put exact-match agreement 33.8 to 41.3 points above Cohen's kappa on MT-Bench, so 85% agreement corresponds to a kappa near 0.48. Declare kappa, show agreement beside it, and name which one the threshold applies to.

Our evaluation set lives in the repository beside the unit tests. What changes?

It becomes evidence rather than fixture code. Article 10 asks whether the test population was representative of the deployment population, and only per item provenance answers that: source, approver, the segment the item stands for, and a contamination check against the training corpus.

Start recording it at admission, since the existing file cannot be back-filled honestly.

We ship monthly. How often does the declared figure have to be re-earned?

Whenever something that moved it changes: a prompt rewrite, a refreshed retrieval corpus, a new base checkpoint from the provider, a new locale, a shift in traffic mix. Version the eval set, the rubric and the judge, pin all three to every figure you declare, and the substantial modification question becomes a query instead of an argument.

How does this differ from your engineering reference on model evaluation?

This report is about what you must declare and later defend, and what a regulator or a customer's auditor can ask you for. Model Evaluation: An Engineering Reference numbers the control families that produce those figures, from the sampling frame through judge validation to the production feedback loop.

Take this one when a declaration is due, that one when you are building the harness.

Who should be reading this one?

Directors of QA and heads of risk who have to sign off a figure that goes into the instructions for use. It assumes you already run evaluations and that the open question is which choices you made on your own authority, and what you kept that proves you made them deliberately.

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Next step

The standard is not here yet and your declaration is due anyway.

Point a two-week trial sprint at the figure you are about to declare, and find out what your evaluation set can prove about the population it was supposed to represent. SECTION 7 - FAQ - 5 to 8 questions

Book an evaluation evidence review