---
title: How Do You Determine Measurement Risk?
description: Understand and manage measurement risk in calibration to ensure reliable results, reduce costs, and protect product integrity with Bagan Calibration Services.
image: https://resource.rjbagan.com/hubfs/How-Do-You-Determine-Measurement-Risk_featured-image_01.jpg
---

# How Do You Determine Measurement Risk?

**Measurement risk** is the probability that a measurement result leads to the wrong decision. In metrology, this usually means either **accepting something that is actually out of tolerance** or **rejecting something that is actually good**. Both outcomes carry cost, compliance, and quality consequences. 

Every measurement contains uncertainty. No instrument, calibration system, or reference standard is perfect. Measurement risk exists whenever that uncertainty is large enough to influence a pass/fail decision. 

Understanding and controlling this risk is essential — especially when evaluating a commercial calibration supplier. 

![How-Do-You-Determine-Measurement-Risk_article-photo_square_01](https://resource.rjbagan.com/hs-fs/hubfs/How-Do-You-Determine-Measurement-Risk_article-photo_square_01.jpg?width=1999&height=2000&name=How-Do-You-Determine-Measurement-Risk_article-photo_square_01.jpg "How-Do-You-Determine-Measurement-Risk_article-photo_square_01")

**What Creates Measurement Risk?** 

Measurement risk is driven by the relationship between three things: 

1. **Measurement uncertainty** 
2. **The specification limit or acceptance limit** 
3. **The decision rule used (Pass/Fail – or conditional Pass/Fail)** 

If uncertainty is small relative to tolerance, risk is low. If uncertainty approaches the tolerance limit, risk rises sharply. 

Additionally, as the measurement approaches the acceptance limits, the risk rises even as the measurement uncertainty stays the same. 

This is why a calibration result without a clearly stated uncertainty is incomplete — and potentially misleading. 

   
 

**Two Direct Types of Measurement Risk** 

Measurement risk is commonly expressed using two statistical probabilities: 

**Probability of False Accept (PFA)** 

The risk of accepting a device or product that is actually out of tolerance. 

**Probability of False Reject (PFR)** 

The risk of rejecting a device or product that is actually within tolerance. 

Both matter, but they affect organizations differently. 

   
 

**Real-World Statistical Examples** 

**Example 1: False Accept (PFA)**

A pressure gauge has a tolerance of **±1.0 psi**. 

The calibration result is **0.8 psi from nominal**, with a **measurement uncertainty of ±0.6 psi (k=2)**. 

Although the reported value is inside tolerance, part of the uncertainty interval extends beyond the tolerance limit. 

Statistical analysis with standard distribution shows there is a **20–25% probability of false accept** — meaning one out of every four gauges is actually out of tolerance, even though it “passed” calibration. 

![Pass decision vs. tolerance when expanded uncertainty overlaps the limit (k=2) 
LSL = - 1.0 psi 
Nominal (0) 
USL = +1.0 psi 
-U 
+U 
Reported = +0.8 psi 
-1.5 
-1.0 
-0.5 
0.0 
0.5 
1.0 
1.5 
Indication error relative to nominal (psi) ](https://resource.rjbagan.com/hs-fs/hubfs/undefined.png?width=800&height=257&name=undefined.png)

**Impact:** 

- Risk of process drift 
- Potential nonconforming product 
- Product recalls 
- Undetected quality issues 

   
 

**Example 2: False Reject (PFR)** 

A torque wrench has a tolerance of **±4 lbf-in**. 

The measured value is **3**.6 lbf-in fr**om nominal**, with a **measurement uncertainty of ±1.5 lbf-in (k=2)**. 

Here, the uncertainty overlaps both sides of the tolerance band. Applying a conservative decision rule may result in rejection. 

Statistical analysis with standard distribution shows there is a **30% probability of false reject** — meaning nearly one-third of rejected tools may actually meet specification. 

![Conservative decision when expanded uncertainty overlaps both tolerance limits (k=2) 
LSL = - 4 lbf.in 
Nominal (0) 
USL = +4 lbf.in 
-U 
+U 
Reported = +3.6 lbf-in 
-6 
-4 
-2 
0 
2 
4 
6 
Torque error relative to nominal (Ibf-in) ](https://resource.rjbagan.com/hs-fs/hubfs/undefined-1.png?width=800&height=258&name=undefined-1.png)

**Impact:** 

- Unnecessary recalibration or repair 
- Increased downtime 
- Higher operating costs 

   
 

**Why Quality Managers Should Care** 

If your calibration provider does not actively manage measurement risk: 

- Passing instruments may still be unreliable, creating customer failures/recalls 
- Good instruments may be removed from service unnecessarily, costing extra money 
- Audit findings may lack defensible technical justification 
- Quality decisions become guesswork instead of data-driven 

A calibration certificate alone does not control risk. **Uncertainty analysis and decision rules do.** 

   
 

**How Measurement Risk Is Properly Determined** 

A competent calibration laboratory evaluates risk by: 

- Developing a **complete uncertainty budget** 
- Comparing uncertainty to **actual instrument tolerances** 
- Applying **defined statistical decision rules** (such as guard banding) 
- Considering **real-world use conditions**, not just bench testing 
- Clearly documenting assumptions and limitations 

This approach aligns with ISO/IEC 17025 and modern risk-based quality systems. 

   
 

**What to Look for in a Calibration Supplier** 

When evaluating a calibration provider, ask: 

- Do they report **measurement uncertainty**, not just pass/fail? 
- Can they explain **PFA and PFR** in practical terms? 
- Do they uncertainty as it relates to **your instrument’s specification (TUR)**? 

If the answers are unclear, your measurement risk probably is too. 

   
 

**Bottom Line** 

Measurement risk is not theoretical — it is statistical, measurable, and manageable. Quality managers who understand **false accept and false reject risk** make better calibration decisions, reduce risk, reduce cost, reduce waste, and protect product integrity. 

A calibration provider’s true value is not in the certificate — it is in how well they control **measurement risk**. 

# You Can Rely on Bagan Calibration Services

We pride ourselves on our premier customer service, which has allowed us to maintain relationships with customers since the beginning. Many of our customers range from Fortune 500 companies to privately owned specialty companies across the U.S.A and other countries. Our proprietary Management Information and Reporting System, BaganTrack gives you direct access to your customer service representative, certificates, master gauge list, and more. Additionally, BaganTrack is compliant to ISO 9001:2015. It is our goal to give you the best experience possible as your calibration and technical service provider.

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