I spent 6 years in the Army as an Interrogator. While we were being trained one of us asked the obvious question: "Why don't we use polygraph machines?" The instructor's answer was short and to the point: "Because they don't work."
As I've gone along, I've come to the conclusion that they are great tools in an interrogation but that they don't actually tell you anything useful. And I'm not alone in this opinion:
Jeffrey Nance, a former undercover cop and author of "Conquering Deception," which examines different ways of detecting lies in everyday life, prefers to bypass the question of scientific accuracy and just think of lie detectors as interrogation tools.This comes from an article about the latest and greatest bit of quackery which has been foisted upon law enforcement - the computer voice stress analyzer.
"I don't think there's a foolproof way to tell if a person is lying or not," Nance told Courttv.com. "There may be people who don't like me saying that but it's the truth."
"It's the fear of the machine that gives it its greatest power," he said. "Even before they get on the machine they may give up information just because [they are afraid] the machine will show that they've lied. And nobody wants to be a liar."
Approximately 1,200 law enforcement agencies use the CVSA, and supporters say that its convenience and accuracy will lead more departments to let their polygraphs, the more well-known truth verifier, start collecting dust.The problem isn't that police use this thing (although I would be irked if my tax dollars were spent equipping the local police with them); the problem is when local police believe in them and make decisions which are based on the machine stating that someone is lying.
But not everyone is enthusiastic about it. In at least a few high-profile cases, the device has appeared to be wrong. And a number of lawyers, civilians and scientists say the CVSA has no scientific validity.
"It's basically a Ouija board," said Nevada lawyer Ian Christopherson, who successfully defended a juvenile probation officer against a rape charge prosecuted largely on the basis of a voice stress test.
And of course there are other machines - past, present, and future - which will be used to try and predict truthfulness with 100% accuracy. We know polygraphs fail this test. "Brain Fingerprinting" has potential but it can only tell if something has been seen before. And "Brain Imaging" is incredibly expensive and appears, so far to only reach 85% accuracy.