1. MARLAP Measurement Uncertainty Workshop
51st Radiobioassay and Radiochemical Measurements Conference
Stateline, Nevada
October 24, 2005

2. 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
I don’t intend to repeat everything we said about MARLAP at last year’s workshop.
I’ll just remind you that…

3. The MARLAP Working Group
EPA
DOD
DOE
DHS
NRC
FDA
USGS
NIST
Kentucky
California
The MARLAP work group had representatives from all the organizations you see listed here.

4. 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 is probably THE key concept in MARLAP’s performance-based approach.
Uncertainty and its importance in MARLAP are the subject of the first half of today’s workshop.

5. 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

6. 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)
It is a property of the measurement process, not just the method.

7. 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)

8. Evaluation of Uncertainty
Most of MARLAP’s guidance for expressing and evaluating uncertainty is in Chapter 19

9. 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

10. The GUM (continued) The GUM is a guide, which presents
Terminology
Notation
Methodology
Includes worked-out examples
Including a radiochemistry example

11. Recommendation Follow the GUM
MARLAP’s primary recommendation regarding measurement uncertainty is
Follow the GUM

12. 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
And NIST would have clobbered us if we didn’t endorse it and follow it ourselves

13. 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

14. 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
And keep mentioning the GUM

15. 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
All times are approximate