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Radionuclides in Drinking Water

Module 6: Determination of Measurement Uncertainty for Radiochemical Analysis


"Statistical Uncertainty" introduces the concept of a measurement as a random variable, and describes how the measurement uncertainty for individual parts of a method can be combined to provide a combined standard uncertainty. It also discusses the method used to estimate the uncertainty based on radiochemical counting of sample test sources and how these combine with other measurement uncertainties associated with the analytical method.

Examples of how to determine a detection limit and equations for MDC and critical level are also presented. The module also provides several calculation examples that need to be attempted so that the overall concept of uncertainties added in quadrature can be better understood.

This module should take between 60 and 80 minutes to complete.

Instructional Resources

This module contains 1 tutorial. It is presented as a self-paced Adobe Flash video with audio narration. The learning aids that are provided for you to use in this module, which you may access via the links in the "Instructional Resources" panel on the right, include the "Multi-Agency Radiological Laboratory Analytical Protocols Manual" (MARLAP) chapter about measurement uncertainty. The EPA "Data Quality Assessment: Statistical Tools for Practitioners (QA/G-9S)" is available from a link under "Links to Additional Information". You may wish to print out the PDF transcript of the audio narration, also available from a link in the "Instructional Resources" panel. The "Links to Additional Information" provide more in-depth discussions of these topic areas.


Tutorial 6.1 - Determination of Measurement Uncertainty for Radiochemical Analysis

At the end of this tutorial you will be able to:

  • Define the terms accuracy, precision, standard uncertainty, and coverage factor as they apply to statistics.
  • Identify measurement parameters that will follow the normal distribution.
  • Calculate the counting uncertainty given the number of counts or the count rate and count time.
  • Identify the various measurements that are made in radiochemical analyses that factor into the final combined uncertainty.
  • Calculate a critical level, MDC, and SDWA detection limit based on counting parameters and sample specific parameters.

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