ISO 17025 Assessments: Defending Your CMC Uncertainty Calculation

Receiving a ‘TBD’ (To Be Determined) during an ISO 17025 assessment can be aggravating. A ‘TBD’ is when an assessor marks one or more portions of your Scope of Accreditation as questionable or incomplete. Typically, this is related to a laboratory’s CMC uncertainty statements. If left unresolved, the ‘TBD’ items are permanently removed from the laboratory’s scope of accreditation.

Accredited laboratories operate within the boundaries of their respective Scopes of Accreditation. It is an important publication that distinguishes one laboratory’s measurement and testing capabilities from another. Furthermore, it exhibits the best measurement uncertainty (quality) that the laboratory is able to achieve. For these reasons, it is important for a laboratory to correctly calculate and convey their CMC uncertainty values.

Challenging an assessor is not an easy task. Most assessors are respected members of the Metrology industry with twenty years or more of experience. Nine times out of ten, your accreditation body is going to support the assessor’s opinion: right or wrong. Therefore, when making the decision to challenge a ‘TBD,’ you must build an effective defense that supports your claim.

To challenge a ‘TBD,’ ask yourself these three questions:

01) What do other labs report?

To check the validity and cohesion of your uncertainty estimates, search to see what other laboratories are reporting. Only compare the values of similar disciplines using similar measuring equipment. This will allow you to perform a direct comparison to the industry accepted estimate of measurement uncertainty. Sample a reasonable number of laboratory scopes (20 is good, if available). Use descriptive statistics to evaluate where your calculations stand in comparison to other laboratories. If your estimates are within the range of accepted values amongst the industry, you stand a good chance to defend your proposal. If not, you are going to need additionally information to support your claims.

02) What do I need?

Before you exert a lot of effort defending your CMC uncertainty calculations, determine what you really need. If your uncertainty values are good enough to accomplish your customers’ calibration and testing requirements, then you may want to reassess your argument. As long as you are able to meet a test uncertainty ratio of four to one or better, you may not need to fight for reduced uncertainty estimates. Unless, you are planning to expand your capabilities to lure new clients, it may not be worth the hassle to go to battle with your accreditation body.

03) Do I have objective evidence?

When making a claim, be prepared to defend it. No matter what you propose, you will always receive some resistance when trying to convince an assessor to accept your CMC uncertainty calculations. The best defensive is objective evidence. Similar to writing a technical paper or journal article, be sure to support your claims with adequate reference material. Never rely on a single source, use redundancy to identify multiple sources of reference material that support each claim. Some great sources of reference material are technical manuals (e.g. manufacture), technical papers, and journal articles. If many of your claims are deduced from empirical research (e.g. experimentation), be sure to keep adequate records of your quantitative data and references for the equations and algorithms used during statistical evaluation. It is hard to dismiss a proposed claim when it is supported through multiple sources of objective evidence.

Answering these three questions can change how you look at your uncertainty estimates. What you discover will either support of the assessor’s concerns, or help you defend your CMC uncertainty proposals. Regardless of the outcome, you will learn more about your laboratory and be better prepared, in the future, for similar scenarios.

When responding to assessors, keep it brief and support your arguments with objective evidence. Only answer the questions that were asked. Do not write long, detailed explanations, they will not be read. Assessors are busy individuals who are managing several assessments at a time. If an assessor rejects your response and you believe that you have effectively proven your case, forgo the assessor and plead your case with the accreditation board.

To search for ISO 17025 accredited laboratories and their Scope of Accreditation, click on the links below.


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About the Author

Richard Hogan

Richard Hogan is the CEO of ISO Budgets, L.L.C., a U.S.-based consulting and data analysis firm. Services include measurement consulting, data analysis, uncertainty budgets, and control charts. Richard is a systems engineer who has laboratory management and quality control experience in the Metrology industry. He specializes in uncertainty analysis, industrial statistics, and process optimization. Richard holds a Masters degree in Engineering from Old Dominion University in Norfolk, VA. Connect with Richard on LinkedIn.

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