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MARLAP Measurement Uncertainty Workshop. 51 st Radiobioassay and Radiochemical Measurements Conference Stateline, Nevada October 24, 2005. Introduction. The Multi-Agency Radiological Analytical Protocols manual (MARLAP) was completed & released in 2004

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marlap measurement uncertainty workshop

MARLAP Measurement Uncertainty Workshop

51st Radiobioassay and Radiochemical Measurements Conference

Stateline, Nevada

October 24, 2005

introduction
Introduction
  • The Multi-Agency Radiological Analytical Protocols manual (MARLAP) was completed & released in 2004
  • Goal: Provide guidance and a framework to assure that laboratory radioanalytical data meet specific needs of a program or project
the marlap working group
EPA

DOD

DOE

DHS

NRC

FDA

USGS

NIST

Kentucky

California

The MARLAP Working Group
the marlap approach
The MARLAP Approach
  • Many have talked about the need for a “performance-based” approach to radioanalytical work
  • MARLAP offers guidance to implement it
  • Measurement uncertainty is a key concept in the approach
uncertainty in marlap
Uncertainty in MARLAP
  • Measurement uncertainty and MARLAP’s derived concept of “method uncertainty” appear throughout the manual
  • Measurement uncertainty defined as a parameter associated with the result of a measurement
  • Method uncertainty defined (in MARLAP) as a performance characteristic of a measurement process
method uncertainty
Method Uncertainty
  • MARLAP defines it as
    • Predicted uncertainty of the result that would be obtained if the method were applied to a hypothetical laboratory sample with a specified analyte concentration
  • The specified concentration is typically the action level
  • Must specify sample characteristics and measurement conditions (as for MDA)
marlap s use of uncertainty
MARLAP’s Use of Uncertainty
  • MARLAP’s performance-based approach uses:
    • Method uncertainty in the selection and validation of a method (Chapter 6)
    • Method uncertainty in the continuing evaluation of a lab’s work (Chapter 7)
    • Method uncertainty and measurement uncertainty in data V&V (Chapter 8)
    • Measurement uncertainty in routine lab QC (Chapter 18)
evaluation of uncertainty
Evaluation of Uncertainty

Most of MARLAP’s guidance for expressing and evaluating uncertainty is in Chapter 19

the gum
The “GUM”
  • In 1993 ISO published Guide to the Expression of Uncertainty in Measurement (the GUM)
    • Developed by 7 international organizations
    • Last revised (corrected) in 1995
  • Purposes:
    • Promote full information on how uncertainty statements are arrived at
    • Provide a basis for the international comparison of measurement results
the gum continued
The GUM (continued)
  • The GUM is a guide, which presents
    • Terminology
    • Notation
    • Methodology
  • Includes worked-out examples
    • Including a radiochemistry example
recommendation
Recommendation

MARLAP’s primary recommendation regarding measurement uncertainty is

Follow the GUM

rationale
Rationale

If everyone follows the GUM:

  • All of us speak and write the same language about uncertainty
  • We can interpret each others results and uncertainty statements
  • Maybe clients can interpret our results and uncertainty statements
additional recommendations
Additional Recommendations

MARLAP further recommends:

  • Labs should consider all sources of uncertainty
  • Evaluate and propagate all uncertainty components believed to be potentially significant
  • Always report the uncertainty
  • Always explain the uncertainty
purpose of this workshop
Purpose of This Workshop
  • Explain uses of uncertainty in MARLAP
  • Reiterate MARLAP’s major recommendations regarding uncertainty
  • Offer approaches and software tools to make uncertainty evaluations easier
outline of the workshop
Outline of the Workshop
  • Part I – Uncertainty in MARLAP
    • Introduction 8:00–8:10
    • Overview of the GUM 8:10–8:40
    • Method Uncertainty 8:40–9:50
  • Break 9:50–10:10
  • Part II – Software tools
    • Kragten Spreadsheet Method 10:10–11:20
    • GumCalc: Measurement Modeling Software 11:20–12:00