A heads up because I think most people don’t realize this: polygraph or “lie detector” tests are absolutely 100% junk science, about as accurate in determining a person’s truthfulness as a flip of a coin would be.
This paragraph from the main article linked above is a perfect sum-up:
The two biggest problems, writes the APA, are these: there’s no way to know if the symptoms of “bodily arousal” (like an elevated pulse) that the machine measures are caused by lies, and there’s no way to know if someone’s results are affected by the fact that they believe in the polygraph machine. If this second view is correct, they write, “the lie detector might be better called a fear detector.”
What I find really bizarre is that although these tests are known to be unreliable enough that they aren’t even admissible in US courts, police seem to actually genuinely believe in them. (Sort of like how they believe they can determine guilt through a suspect’s body posture, gestures, or “micro expressions” during interrogation.) They also very clearly take refusal to subject yourself to a polygraph as proof of guilt, just like they’ll take the results of the polygraph as proof of guilt, even though both are terrible metrics for determining those things. Government agencies, like the FBI and CIA, are even still allowed to use polygraphs to screen potential employees, even though the results of these tests are known to be unreliable.
This info is useful if you’re ever suspected of a crime – NEVER consent to a polygraph, even if you’re 100% innocent, even though it will make police think you’re hiding something – but also just as general information. Like if you’re a writer of crime thrillers, you can absolutely depict a cop as taking a polygraph failure as proof of a suspect’s guilt, because that’s pretty accurate, but you probably don’t want to make the narrative itself support that as some sort of scientific or irrefutable truth, because it definitely isn’t, and perpetuating the idea of the polygraph’s mythic and impossible ability to somehow detect deception is literally harmful to society.
Two things about this:
In America, basically just don’t talk to the cops at all if you’re a suspect, especially if you’re innocent. You shouldn’t even get to the point of them asking if you’ll take a polygraph test, because the only answer to every question you need to know is “Lawyer”. Or if you’re feeling up for it, a more friendly, full phrasing.
In my first-hand experience cops are really good at selectively taking everything you say as evidence of whatever idea they already have in their head. Maybe even better at this than normal people on average, I’m not sure.
I have links to a video somewhere if anyone’s interested of a defense lawyer thoroughly lecturing some law students about this, followed by a police detective basically saying that the defense lawyer is totally right: Talking to the police if they already suspect you basically can only hurt you. Lawyer up immediately.
Here’s the key thing that you need to know about a lie detector test: The lie detector itself detects general biological activity, which includes your body’s reactions to stress and fear.
A lie detector test “works” by trying to psych you out into being afraid of it working.
Basically, they will tell you exactly the list of questions they’re going to ask you, in the order they’ll ask them. They will go over the questions with you, and your answers, before the actual test, often multiple times.
The idea is this: it’s assumed you’ll have an anticipation-driven build-up of stress response in the lead-up to the questions that you’re going to lie about, and an immediate relief-drive drop in stress response after you’ve answered the question you’re going to lie on.
They will explain all of this to you too, because the whole charade only half-works if you believe it does.
They will not explain to you the obvious problems:
- If you genuinely don’t feel concerned about being caught, etc: no expected stress response around the lies.
- If you are just worried about the obvious “did you kill Bob” question, because you know you’re being suspected of having killed Bob or because you have a strong emotional reaction to the thought of Bob being dead, you can have a similar response without lying.
So if you can just relax and remember that you could literally lie out your ass and it won’t detect shit so long as you’re not worried about lying, and don’t work yourself up as the “significant” questions are coming, it indeed won’t detect shit.
If you can’t maintain that attitude, you can freak yourself out erratically the entire time during the test (maybe dive as mentally deep as you can into any phobias or past traumas or anger-inducing shit as you can), and then their little graphs will be all over the place through the entire test, and the test is deemed “inconclusive”.
So if you’re ever forced/coersed into taking one, hopefully this gives you better odds of not being wrongly implicated by the results.
The funny thing is, the replacement for polygraphs can still be beaten by a large percentage of criminals. An fMRI is only valid as long as the person has to spend effort to lie, and as such, doesn’t work very well on pathological liars.
But seriously, in the US, your only words to the cops should be “Where’s my lawyer?” or “I exercise my fifth amendment right to say nothing until my lawyer is present.”
Outside the US, you’re probably fucked either way unless you’re a semi-permanent resident or a citizen in that country (or in another EU country because that shit is weird).