“When Lie Detectors Lie – Or Don’t”

Richard A. Muller, a physics professor at the University of California, Berkeley, writes for Technology Review. Erroneously assuming that polygraphy is a valid diagnostic technique with an 85% accuracy rate, and ignoring the issue of countermeasures, Muller concludes that polygraph “evidence” should be admissible in court:

Now we come to the true paradox. Lie detector results are inadmissible as evidence for criminal trials in most states. But I have been present at a trial in which the judge instructed the jury that it was their responsibility, not his, to determine the truth of the testimony. To do this, they were told to take into account “the demeanor” of the witness, his directness in answering questions, and anything else that they thought indicated truthfulness. Ironically, scientific tests show that the average person’s probability of catching a lie in this way is only “slightly better than chance,” according to Ekman. Moreover, the jurors who use this approach have the conviction that their accuracy is near 100 percent, despite their knowledge that most witnesses are extensively coached in methods of appearing sympathetic and truthful–in other words, in methods to defeat the system.

Polygraphy is not allowed in courts because 85 percent accuracy is not good enough. Instead courts use a system that is demonstrably worse–which could be a big part of the reason why so many convictions are now being overturned by DNA evidence. Where is the wisdom in that?

The Technology Review website includes a forum for discussion of articles, where George Maschke of AntiPolygraph.org has posted a response.

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