Last Updated on September 25, 2025 by Melissa Lazaro

ISO/IEC 17043:2023 Glossary – Essential Terms You Should Know

Let’s face it—reading ISO standards isn’t anyone’s idea of light reading. Even if you’re experienced, sometimes you pause and think, “Wait, what exactly do they mean by that?”

Over the years, I’ve worked with plenty of labs and PT providers implementing ISO/IEC 17043. And here’s what I’ve noticed: the real challenges often start with the words. Not the requirements themselves—but how people interpret terms like assigned value, reference value, robust statistics, or even impartiality.

That’s why this glossary exists.

Whether you’re updating your documentation, onboarding a new team member, or preparing for an audit, this article will walk you through the essential terms in ISO/IEC 17043:2023—in plain language, with real-world context.

Let’s start with the basics and build from there.

Core Terms You’ll See Throughout the Standard

Proficiency Testing (PT)

This is the whole point of ISO/IEC 17043. PT is a process where multiple laboratories analyze the same sample under the same conditions—and their results are compared to assess performance.

It’s how labs prove that their test results are accurate, consistent, and traceable.

Why it matters:
PT is one of the most widely accepted tools for demonstrating technical competence—especially for ISO/IEC 17025-accredited labs.

Interlaboratory Comparison (ILC)

An ILC is any activity where the same or similar items are tested by multiple labs and their results are compared. PT is a specific type of ILC with performance evaluation built in.

Key difference:
All PTs are ILCs—but not all ILCs are PTs. PT must include formal evaluation criteria.

Participant

A lab, organization, or facility that takes part in a PT scheme. These are the end users being evaluated.

What to remember:
Participants rely on your design, instructions, and evaluations to reflect their performance fairly.

PT Provider

The organization responsible for designing, operating, and evaluating the PT scheme. If you’re reading this article as a provider, this is you.

Your responsibilities include:

• Scheme planning
• Sample distribution
• Data collection
• Statistical evaluation
• Reporting and confidentiality

Assigned Value

This is the value used as the basis for evaluating participant results. It represents the “target” or reference against which labs are scored.

Important note:
The assigned value must be based on reliable data—this could be a reference material, a consensus value, or a measurement by an expert lab. It must also be traceable or justified.

Reference Value

Sometimes confused with the assigned value, but subtly different. A reference value is often linked to certified reference materials (CRMs) or traceable calibration values.

Best practice:
If your assigned value comes from a CRM, your reference and assigned values may be the same. But if not, be clear about how they differ—and why.

z-score, En value, and robust statistics

• z-score: A standard deviation-based score used to evaluate how far a lab’s result is from the assigned value.
• En value: Often used in calibration PT, comparing lab result uncertainty to assigned value uncertainty.
• Robust statistics: Methods that reduce the influence of outliers in performance scoring.

Why it matters:
Choosing the right evaluation method shows technical competence and fairness.

Homogeneity and Stability (of PT items)

Before you send out PT samples, you need to prove that they’re homogeneous (the same across all samples) and stable (won’t degrade before use).

Auditor expectation:
They’ll want to see validation records or studies that confirm your samples meet both criteria.

Scheme Design & Evaluation Terms You Should Know

Scheme Plan

This is the full design of the PT round. It includes timelines, sample types, instructions, evaluation criteria, and communication strategy.

Tip:
Don’t keep the plan in your head—document it. Auditors want to see it written down and shared with participants (appropriately).

PT Item

The sample, material, or artifact sent to participants for testing.

Could be:
Soil, blood, water, calibration weight, or even a questionnaire—whatever fits your scheme.

Instructions for Participants

Every scheme should include clear, written instructions telling participants:

• How to handle and test the item
• What data to submit
• How to report results
• Deadlines

Why this matters:
Ambiguous or missing instructions are a common nonconformity during accreditation audits.

Statistical Design

This refers to how your PT scheme is structured for meaningful analysis. It includes sample size, type of distribution, scoring model, and uncertainty handling.

Your responsibility:
Use appropriate, documented methods—and be ready to explain why you chose them.

Evaluation Criteria

How you’ll determine whether a participant’s performance is acceptable. This must be defined before the scheme begins.

It should be:
Relevant, fair, traceable, and tailored to the type of test or measurement.

Measurement Uncertainty (MU)

MU isn’t just for labs—it also matters when you’re assigning values and evaluating participant performance.

If you’re using En values:
You’ll need to include your own MU in the calculation and justify it with traceable references or data.

Roles, Responsibilities & Risk Terms in ISO/IEC 17043

Impartiality

The PT provider must be free from bias—especially when designing schemes, selecting evaluators, or analyzing data.

Tip:
If your staff are also participants, or if you have commercial ties to any lab involved, document how you’re managing that risk.

Confidentiality

Participants’ identities and results must be protected.

Watch out for:
Leaky Excel files, careless emails, or poorly secured report sharing platforms. Confidentiality isn’t just about policy—it’s about practice.

Subcontractor / External Provider

If you outsource testing, sample prep, or logistics, that party becomes a subcontractor under ISO/IEC 17043.

Make sure you:

• Evaluate their competence
• Document the relationship
• Keep control of quality and impartiality

Top Management (in PT context)

Not just the CEO. This refers to the individuals responsible for the overall function, quality, and impartiality of your PT program.

What auditors want:
Clear roles, delegated authority, and evidence that top management is involved and accountable.

Decision Rule

This is the logic you apply when interpreting participant performance. It answers: “When is a result acceptable or not?”

Why this matters:
A clear, documented decision rule ensures consistency—and fairness.

Risk-Based Thinking

ISO/IEC 17043:2023 expects PT providers to proactively identify, assess, and manage risks.

Examples include:

• Late shipments
• Data breaches
• Ambiguous instructions
• Unjustified scoring models

Tip:
Keep a simple risk register. Show that you think ahead—not just fix issues afterward.

Pro Tips for Using These Terms in Your System

Pro Tip: Use the same terms across your QMS

Avoid confusion by aligning your SOPs, forms, and training materials with the standard’s language.

Pro Tip: Include the glossary in your onboarding kit

Make it part of your staff training—not just a reference during audits.

Pro Tip: Build a “terms in action” folder

For each key term, keep a live example: an actual PT item plan, a homogeneity study, an evaluation method, etc.

Common Mistakes to Watch Out For

• Using “assigned value” without explaining how it was set
• Assuming all z-scores are created equal—context matters
• Skipping uncertainty estimation because “it’s just PT”
• Using evaluation methods with no reference to statistics
• Thinking confidentiality is handled just by “password protecting” one folder

These are the kinds of issues that pop up in real audits—and they’re easy to avoid with better understanding.

FAQs – Quick Answers to Common Questions

What’s the difference between assigned value and reference value?
The assigned value is used to evaluate participant results. A reference value is often traceable to a standard like a CRM. Sometimes they’re the same, but not always.

Are interlaboratory comparisons and proficiency testing the same thing?
Not quite. All proficiency testing is an interlaboratory comparison, but not all interlaboratory comparisons include performance scoring—PT does.

Do I have to use z-scores in every scheme?
No. You can use other statistical tools like En values or expert judgement—as long as the method is appropriate and clearly documented.

Do I need to define a decision rule for my PT scheme?
Yes. Every PT scheme should explain how performance is evaluated—what’s considered acceptable, and why.

What if my PT samples aren’t perfectly stable or homogeneous?
That’s okay—as long as you document the limitations, explain the risks, and validate them as best you can.

Speak the Same Language as the Standard

ISO/IEC 17043:2023 is built on clarity, structure, and trust. And that trust starts with using the right language, consistently and intentionally.

When you and your team know what these terms mean—not just academically, but practically—you:

• Run stronger schemes
• Pass audits with fewer surprises
• Help participants improve with clarity and confidence

Want this glossary in a downloadable format for internal use or training? I can create a clean, print-ready version or even help customize it for your organization’s QMS.

Let’s make ISO language second nature—not a source of confusion.