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Measurements should not be recorded as less than MDA: an extension
William Edward Potter1, Jadwiga Strzelczyk
1pspr189729@aol.com
Health Physics
|June 14, 2008
Summary
Reporting radioactivity measurements as "less than minimum detectable activity" is incorrect. This study explains why and extends methods for accurate radioactivity measurement reporting, even with unequal counting times.
Area of Science:
- Radiochemistry
- Nuclear Measurement Science
- Analytical Chemistry
Background:
- Radioactivity measurements are frequently reported as "less than the minimum detectable activity" (MDA).
- Previous literature has highlighted the incorrectness of using "less than MDA" for reporting measurement results.
- This work addresses the statistical underpinnings of radioactivity detection limits.
Purpose of the Study:
- To explain why reporting radioactivity measurements as "less than the minimum detectable activity" is statistically inappropriate.
- To extend existing methodologies for radioactivity measurement reporting to scenarios with unequal counting times for blank and sample.
- To provide a statistically sound basis for interpreting radioactivity measurement results.
Main Methods:
- Review of historical perspectives on reporting radioactivity measurement results.
- Statistical analysis of radioactivity detection, focusing on the decision level.
- Extension of paired counting methods to accommodate variable blank and sample count times.
- Development of a framework for reporting radioactivity measurements that avoids the "less than MDA" fallacy.
Main Results:
- Demonstration of the statistical flaws in reporting results as "less than the minimum detectable activity."
- Establishment of the decision level as a critical parameter in radioactivity detection.
- A generalized method for radioactivity measurement reporting applicable to diverse counting time scenarios.
- Improved accuracy and interpretability of radioactivity measurement outcomes.
Conclusions:
- Reporting radioactivity measurements as "less than the minimum detectable activity" is statistically unsound and should be avoided.
- The decision level provides a robust threshold for claiming detection of radioactivity.
- The extended methodology offers a more accurate and reliable approach to reporting radioactivity measurements, particularly when blank and sample count times differ.
- Accurate reporting of radioactivity measurements is crucial for reliable scientific interpretation and regulatory compliance.
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