Last Updated on December 22, 2025 by Melissa Lazaro

Why Statistical Review and Homogeneity Matter in ISO/IEC 17043

If there’s one area that makes PT providers uneasy during audits, it’s statistics.

Not because the maths are wrong—but because the logic behind the maths isn’t always explained.

In my experience, most ISO/IEC 17043 statistical findings don’t come from incorrect calculations. They come from weak justification. Auditors ask why a method was used, and the answer isn’t clear or documented.

This article focuses on two closely linked areas:

• Statistical review, and
• Homogeneity assessment

Both sit at the heart of Clause 7. And both are frequent sources of audit findings when they’re treated as technical side notes instead of controlled processes.

The Role of Statistical Review in ISO/IEC 17043 Proficiency Testing

Statistical review isn’t just a final check before issuing PT results.

Under ISO/IEC 17043, it’s a control mechanism.

Auditors expect statistical review to confirm that:

• The chosen statistical methods are appropriate
• The assigned value makes sense for the scheme
• Performance evaluation is consistent and justified
• Results support reliable conclusions

Here’s where things often go wrong.

Providers assume that because results were generated by software, they’re automatically valid. Auditors don’t see it that way.

Pro tip:
Statistical review should explain decisions, not just confirm calculations.

Common mistake:
Treating statistical review as a signature step instead of an independent evaluation.

ISO/IEC 17043 Homogeneity Assessment – Why It Can’t Be an Afterthought

Homogeneity assessment answers a simple but critical question:

Are all participants really testing comparable items?

If the answer isn’t clear, everything that follows—assigned values, z-scores, performance conclusions—becomes questionable.

Auditors look closely at homogeneity because it directly affects:

• PT scheme credibility
• Statistical validity
• Fairness of participant evaluation

I’ve seen audits slow down fast when providers rely on supplier assurances alone.

Pro tip:
Supplier data can support homogeneity—but it rarely replaces provider responsibility.

Common mistake:
Assuming homogeneity is implied because items came from the same batch.

Designing Homogeneity Studies for ISO/IEC 17043 Compliance

Homogeneity studies don’t need to be complicated—but they do need to be defensible.

Auditors expect to see:

• A clear sampling plan
• Defined number of test portions and replicates
• Suitable measurement methods
• A rationale that matches the PT item and risk

Over-engineering studies can raise as many questions as under-doing them.

In my experience, the strongest homogeneity studies are:

• Simple
• Proportionate
• Clearly documented

Pro tip:
Design homogeneity studies so you can explain them in plain language.

Common mistake:
Copying study designs from unrelated PT schemes without justification.

Statistical Methods Used in ISO/IEC 17043 Homogeneity Assessment

Auditors don’t expect every PT provider to use the same statistical tests.

What they do expect is clarity.

They want to understand:

• Which statistical method was used
• Why it was suitable
• How acceptance criteria were defined
• What decisions were taken based on results

I’ve seen providers lose confidence when auditors ask, “Why this method?” and the answer is simply, “That’s what we’ve always used.”

Pro tip:
Document the reasoning behind your statistical choices, not just the results.

Common mistake:
Using formulas without explaining their applicability to the PT item.

Statistical Review of PT Scheme Results Under ISO/IEC 17043

Statistical review doesn’t stop with homogeneity.

It continues through:

• Assigned value determination
• Performance scoring
• Outlier treatment
• Interpretation of overall scheme performance

Auditors often trace one PT round from start to finish. They want to see consistency.

This is where weak documentation shows up.

Pro tip:
Link statistical review records directly to PT scheme decisions and reports.

Common mistake:
Separating statistical analysis from technical review and approval.

Common ISO/IEC 17043 Audit Findings Related to Statistical Review and Homogeneity

After reviewing many audit reports, certain findings appear again and again.

Common issues include:

• Homogeneity assessment not clearly justified
• Statistical review performed by someone without demonstrated competence
• No evidence of independent review
• Acceptance criteria applied inconsistently

These findings usually aren’t about intent—they’re about control and clarity.

Pro tip:
Use internal audits to challenge your statistical assumptions before auditors do.

Common mistake:
Treating statistics as a specialist area outside the management system.

FAQs – ISO/IEC 17043 Statistical Review & Homogeneity Assessment

Is homogeneity assessment required for every PT scheme?
Not always. The need depends on the PT item, scheme design, and risk—but the decision must be justified.

Who should perform the statistical review under ISO/IEC 17043?
Someone competent and, where possible, independent from scheme execution. Competence must be demonstrable.

How detailed should statistical documentation be for audits?
Detailed enough to explain decisions clearly. Auditors value clarity over complexity.

Conclusion – Making Statistical Review Work for ISO/IEC 17043 Compliance

Statistical review and homogeneity assessment don’t need to be intimidating.

When PT providers:

• Treat statistics as controlled processes
• Document decisions clearly
• Match study design to risk
• Integrate review into the management system

…Clause 7 audits become far more predictable.

I’ve seen PT providers move from repeated statistical findings to clean audits simply by improving explanations—not calculations.

Your next step:
Review your statistical review and homogeneity processes with an auditor’s mindset. If you can explain why you do what you do, you’re already ahead.