yankeedog wrote on Jun 3^rd, 2008 at 12:19am:

Or, you “could” have been a false positive.  It doesn’t happen often, but it does happen.

The best field studies of polygraphy suggest that a truthful person may have roughly a 50-50 chance of passing a polygraph "test." See Dr. Alan Zelicoff's "Positive and Negative Predictive Values of Polygraphs: Results from published 'field' studies":

https://antipolygraph.org/articles/article-051.pdf

and also Dr. Michael Langan's "The Art of Deception: Polygraph Lie Detection":

https://antipolygraph.org/articles/article-053.shtml

Langan notes that "if a medical test had a similar sensitivity and specificity to that of the polygraph examination it would simply not be used in the field of medicine." And Zelicoff has elsewhere observed, "If we had medical tests that had the same failure rate as a polygraph, then physicians that use those tests would be convicted of malpractice."