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FailureToReason t1_j2857l7 wrote

Short answer: they're not accurate, can be easily fooled, and are basically inadmissible because they have a very weak scientific foundation

What they ARE good for, is manipulation. You swear up and down you didn't kill your wife. Detective asks, 'would you take a polygraph?' And you start sweating bullets. You complete the polygraph, and the polygrapher comes in and tells you 'I know you lied to me.' And maybe they do, or are at least suspicous because of your body language or evidence that contradicts you. But in that moment, under that pressure, people crack.. The cop may have absolutely nothing, and is just fondling in the dark. 'I know you lied on some of these questions.' Next thing you're confessing to a triple homicide that you may never have been caught for.

Edit: body language isn't necrssarily evidence, corrected the phrasing there.

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allthejokesareblue t1_j285z9y wrote

>by body language

Which is also highly inaccurate

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FailureToReason t1_j288njg wrote

Absolutely, but let's not ignore that large part of criminal investigation is 'gut feel' and instinct, and both the polygraph and body language are useful for what they are useful for, but neither is valuable as incriminating evidence. There have been plenty of people who acted guilty as sin but were completely innocent, and plenty of psychopaths who seemed completely innocent until a compelling piece of evidence blew the investigation open.

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LordJadex t1_j28asv5 wrote

It’s almost like they want people confessing to crimes they didn’t do. Tactics like this cause that to happen constantly. When under immense stress people will confess to get the stress to go away whether they did it or not.

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