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Bob Park of the American Physical Society writes the following in the 4 January 2002 installment of his What's New column:
Quote:
3. AIRPORT LIE DETECTOR: AT FIRST BLUSH, IT'S A DUMB IDEA. The system is supposed to scan the faces of passengers at the check- in counter with a high-definition thermal imaging camera while they answer questions. The claim is that blood rushes to the eye area when people lie. That may be, but your face will also flush when you run three miles from Concourse A to Concourse F, only to find the gate has been changed. On the other hand, you may turn pale if you see fuses dangling from another passenger's shoes. In short, it will work as well as a polygraph, which is not at all.
Posted by: G Scalabr Posted on: Jan 7th, 2002 at 9:17pm
Yes, this device does indeed seem to be plagued with the same problems as polygraphy. Most importantly, the "base rate" problem would make it completely useless in an airport setting.
I’m going to be generous and estimate that the base rate of terrorists to legitimate passengers is 1 per 1,000,000. The UPI article reports that the device is 80 percent accurate. This means that the "test" is 80/20 (percentages) with liars and 80/20 with truthful people. When that one terrorist comes through, there will be an 80% chance that he will set it off. On the other hand, 200,000 truthful people will be falsely accused. So for every terrorist that comes through, we still have to pick him out of the 200,000 innocent people who have also set the device off. Thus, the chance of catching a terrorist with this test (its predictive validity) would be .0005 (or 5/1000 of a percent). On the other hand, I could simply declare everyone truthful and my prediction would be 99.9995 accurate.
As Fred F said in another thread, all this device would do in airports is create chaos.
Posted by: beech trees Posted on: Jan 7th, 2002 at 7:57pm
It seems to me that Dr. Levine has drawn conclusions that go far beyond the evidence of his research. For example, his thermal imaging camera did not detect "lying," as the Mayo Clinic news release claims. Rather, lying was inferred based on increased temperature of the eye sockets. This technique seems likely to be beset with the same problems as polygraphy.