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Technical Discussions
Terry Oldberg
Engineering, Mechanical Electrical Nuclear Software
Consultant, USA, Joined Oct 1999, 42

Terry Oldberg

Engineering, Mechanical Electrical Nuclear Software
Joined Oct 1999
08:24 Sep-06-1999
Unit Measure violations in "The TOFD Method..."

The test described by A. Erhard and U.Ewert in "The TOFD Method..." (NDTnet, September 1999) is a flaw detector. Thus, it must violate the Unit Measure axiom of probability theory in relation to theories of its reliability (see "Erratic Measure," http://www.ndt.net/article/v04n05/oldberg/oldberg.htm ) Yet the authors of "The TOFD Method..." present the results of their research as a probabilistic theory of the test's reliability. It follows that this research was doomed before it was undertaken.

The inconsistency of the test with a probabilistic theory of its reliability would be revealed if the authors of "The TOFD Method..." were to provide details about the methodology of the reseach that are omitted from their paper. In particular, the inconsistency between the test and the theory of its reliability that is presented in "The TOFD Method..." would be revealed if the authors were to:
1. Describe the study's statistical population.
2. Describe the partition that divides this population into sampling units.
3. Describe the "frame" or list of sampling units from which the study's sample was drawn.
4. Describe the procedure by which the study's sample was selected from the frame.
5. Describe the rule under which each sampling unit in the sample was judged a positive or negative event by the TOFD test.
6. Describe the rule under which each event under item 5. was judged truly positive falsely positive, truly negative or falsely negative.
7. Describe the relationship between the set of (truly positive, falsely positive, truly negative and falsely negative) events that are generated byh the test and the set of sampling units. Is this relationship one-to-one? If so, Unit Measure is preserved. Otherwise, it is violated.
8. Describe how the probability of detection is computed.
9. Discuss the omission of a probability of false call from the paper's findings.


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