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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