measurement uncertainty workshop · 2019. 11. 7. · measurement uncertainty workshop • welcome...

MEASUREMENT UNCERTAINTY WORKSHOP

Lab Accreditation Meeting St. Petersburg, FL.

Jan. 24th 2017

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Measurement Uncertainty Workshop

• Welcome

• Sue Humphries, Acting Quality System Manager, Office of Regulatory Affairs, Pacific Regional Laboratory Northwest, U.S. Food and Drug Administration

• Patricia Hanson, Biological Administrator l-Microbiology Supervisor, Bureau of Food Laboratories, Florida Dept. of Agriculture and Consumer Services

• Heidi Hickes, Bureau Chief, Analytical Laboratory Bureau, Montana Dept. of Agriculture

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Outline•What is Measurement Uncertainty (MU)

•Why does ISO 17025 care about MU

•ISO17025 requirements

•Microbiology/Chemistry MU examples applied in real LAB setting

•Volunteers for hands on MU determinations

•Take Away MU messages

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What is Measurement Uncertainty ?

•When repeated measurements give different answers

•How widely spread are the values—wiggle room

•Judge quality of measurement from the spread

•Measure AVERAGE and STDEV in EXCEL

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What is Measurement Uncertainty ?

•Standard deviation-quantify spread

•STDEV expressed in units measuring

•%RSD: Relative Standard Deviation

•%RSD=divide STDEV by AVERAGE multiply by 100

•Universal Unit

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Why does ISO 17025 care?

•Measurements are subject to errors.

• Measurements have uncertainty associated with it.

•Result is incomplete without a statement of MU.

• Without MU give wrong impression to customer

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ISO 17025 Requirements

•Requires MU be estimated for your method

• Requires procedures to estimate MU

• Identify all components of uncertainty

• Follow conventional methods

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ISO 17025 Requirements

• Make Reasonable estimation of MU

• Express uncertainty values consistently and properly

• Ensure report does not give wrong impression of uncertainty

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ISO 17025 Requirements

• Need to put a number to the uncertainty

• Understandable and relevant

• You do not have to hire a statistician!

• Reasonable estimation based on method

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Practical and User Friendly

•Become familiar with uncertainty language

•Become familiar with basic steps

• Follow conventional methods

•Make a Reasonable Estimation

• Traceable: others need to understand what was done

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“A person who never made a mistake never tried anything new.”

Albert Einstein

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Take Aways• ISO requires MU be determined for each method

• ISO require procedures for determining MU

• Follow conventional methods

• Expressed properly

• Understandable and usable

• Traceable

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