MARLAP Measurement Uncertainty Workshop

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

3. EPA DOD DOE DHS NRC FDA USGS NIST Kentucky California The MARLAP Working Group

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

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)

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 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

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

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