Human lie detectors are wrong as much as they are right

While investigating my first wrongful conviction case after my book Presumed Guilty was published in 1991, I was shocked to learn that the FBI “expert” who polygraphed defendant Paul Ferrell was allowed to testify that Ferrell had given a nonverbal confession. According to the agent, Ferrell nodded his head as the agent discussed why investigators believed Ferrell had killed a missing woman. Although Ferrell insisted he was innocent, the agent said his slight head nod was an admission of guilt.

Ferrell’s appeals attorney argued in his brief that this was apparently the first time such testimony had been admitted in American court and should have been disallowed. The appeals court agreed, but called the admission “harmless error.”

When I called Paul Ekman, the leading authority on nonverbal communication, to discuss the FBI polygraphist’s testimony, he expressed dismay. Ekman said the body-language interpretation of FBI polygraphists had been repeatedly shown in studies to be wrong about half the time. Even worse, he said, head nods are the most difficult of all body motions to interpret.

Ekman sounded like the voice of reason then. Unfortunately, a few years later, Ekman developed the Facial Action Coding System, which he claimed can be used to determine whether someone is lying with 95 percent accuracy. Law enforcement quickly moved to adopt the system, which was featured on the American TV series, Lie to Me, whose main character was an expert on divining deception based on Ekman.

But as Sue Russell points out in an article that’s part of her excellent series on wrongful convictions in Pacific Standard magazine, that’s bad news for innocent suspects. Regardless of the training people use to convince themselves that they can tell when someone is lying, Russell says, “research repeatedly shows that confidence to be misplaced.” You can read her story here.

One response to “Human lie detectors are wrong as much as they are right

  1. Marty,
    Great article. This is exactly how the Reid Technique starts out – with the so-called “behavioral analysis interview”. During this phase the police interrogator decides whether or not the suspect is telling the truth. If the interrogator decides the suspect is lying/guilty, the interrogation method switches to the adversarial mode. And guess what – the decision is made based upon all the unsupported, and likely ‘wrong’, indicators that you point out.

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