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

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…

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.

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.

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 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.

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

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 is a guide, which presents Terminology Notation Methodology Includes worked-out examples Including a radiochemistry example

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

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

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 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

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