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The Debunker: Do Lie Detectors Detect Lies?

by Ken Jennings

In February, Americans celebrate the birthday of George Washington and Abraham Lincoln—not just beloved leaders but famous symbols of truth-telling as well. Washington wouldn't even lie about his child vandalism of cherry trees (even if that story never really happened) and Abraham Lincoln was "Honest Abe," a lifelong symbol of candor and integrity. Jeopardy!'s Ken Jennings believes that honesty is the best policy, so he's here all February to tell us the truth about the art of lying.

The Debunker: Do Lie Detectors Detect Lies?

The story of the modern "lie detector" test began in 1920 with psychologist William Moulton Marston. He theorized that measuring systolic blood pressure could predict a subject's emotional state. Later in life, after a police officer in California had adapted this test into the first polygraph machine, Marston became much more famous for his work in, of all fields, comic books. He created the superhero Wonder Woman for DC Comics, and even gave her a Lasso of Truth. This was a handy accessory that combined Marston's two great loves: lie-detecting, and bondage.

The Debunker

But the so-called "lie detector" test, despite its name, doesn't really detect lies at all. By recording heart rate, respiration, and skin conductance ("sweating," in less technical terms), a polygraph is doing one job: keeping a record of heart rate, respiration, and skin conductance. Polygraphs are autonomic arousal detectors, sure. But there's not really any evidence that lying is a unique cause of any particular autonomic arousal.

That's why U.S. Supreme Court cases since 1923 have ruled polygraph tests as inadmissible in court: there's still no scientific consensus that they are reliable. They may predict deception better than you could by flipping a coin, but there are still significant problems with their results. They are extremely prone to false positives, for example, because many people taking a polygraph test get worked up into a state of anxiety even if they're telling the truth. And the American Psychological Association notes that there are plenty of effective techniques that can allow a liar to defeat a polygraph, from physical movements to mental training to pharmaceutical agents. Finally, the theory that all deception requires active, conscious effort (and will therefore produce physical arousal) is now pretty outdated. The human conscience is a weird kingdom, and there's a whole continuum of untruth that passes through a lot of gray areas before it passes into the realm of overt lies.

It's tempting to believe that there's a science-y solution that will map all these gray areas and defeat the scary specter of deception in general, but so far, researchers in that quest have come up short. Next time someone makes sweeping claims to you about the effectiveness of "lie detectors," get out your B.S. detector.

Quick Quiz: Gary Ridgway, who had passed a polygraph test in 1984, was arrested in 2001 as the serial killer associated with what Washington State river?

Ken Jennings is the author of twelve books, most recently Planet Funny and co-hosts the most important podcast in human history, Omnibus. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at or on Twitter as @KenJennings.