Polygraphs, at best, potentially measure nervousness. The assumption is that lying makes people more nervous than telling the truth.
As others have said, the science behind this is bullshit.
this post was submitted on 29 May 2025
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I've taken 3 polygraphs in my lifetime, and I lied on all three. None of the polygraphers caught the lies, but all three accused me of lying on other questions where I told the truth.
Polygraphs are voodoo. I might take one for a job, if it were required, but I would never agree to one for the police. I would NEVER trust my freedom to one.
They don't work.
They measure a bunch of vital information, but they are wrong almost as often as they are right. They're total garbage
Not only are they made up indicators, they are operated by someone who does a subjective reading of the output!
They're actually only about 48% accurate, meaning that they're more often wrong than right and you are 2% more likely to guess the right answer.
For this reason, they are inadmissible as evidence in court in Canada and the US, and possibly other places too.
They're actually only about 48% accurate, meaning that they're more often wrong than right and you are 2% more likely to guess the right answer.
Wait what are the Bayesian priors? Are we assuming that the baseline is 50% true and 50% false? And what is its error rate in false positives versus false negatives? Because all these matter for determining after the fact how much probability to assign the test being right or wrong.
Put another way, imagine a stupid device that just says "true" literally every time. If I hook that device up to a person who never lies, then that machine is 100% accurate! If I hook that same device to a person who only lies 5% of the time, it's still 95% accurate.
So what do you mean by 48% accurate? That's not enough information to do anything with.
They flat out DON'T work at all in detecting lies. Well documented as total fraud. Polygraph just means 'many graphs', which is all they produce: many graphs of sensors output not having anything to do with honest or dishonest responses.
many graphs of sensors output not having anything to do with honest or dishonest responses.
Well, they sense physiological changes associated with dishonesty (stress/nervousness). The problem is they can't pick up false positives (someone being honest despite being nervous under interrogation) or false negatives (someone who can remain totally unfazed while being dishonest).
So while technically they do have something to do with honest/dishonest responses, it's nowhere near a direct enough correlation to be useful for the purpose.
The changes they pick up on are responses to a lot of different things, not just lying, so even the premise is fatally flawed.
That's what I meant by "false positives". They are measuring responses related to lying, but not exclusively and not reliably.
I wasn't correcting you, or saying otherwise. Just condensed version of what you said, and adding that it just makes the whole idea flawed from the outset.
Yeah, but they circle parts of the graphs with red pen so it must be real!
Lie detectors can't determine the truth. They can only tell if you're nervous about something. They monitor heart rate, breathing, skin temperature and perspiration levels. They can see when these factors change when asked specific questions, which may indicate that you are lying...but it's really a matter of the kinds of questions they ask, and how your reactions are interpreted. They are not considered reliable.
This. They measure these body changes and some idiots decided that these correlate perfectly with lies, but really they can correlate with plenty of things. They start with a base measurement where they ask you simple and verifiable questions such as your name, address, etc.
Here are some legitimate reasons that can get you marked as a liar:
- Getting nervous because you are being investigated.
- An accusatory question gets you nervous
- Panic attack
- Physical discomfort, can be because of a long investigation.
- A question agitates you
- And more
A polygraph can be useful to help uncover the truth as it can help investigators possibly find subjects that disturb you and could relate to lies.
Calling a polygraph a lie detector is ignorant, malicious, stupid, or some combination of the above.
P. S
Good liars can fool polygraphs easily, like not even a complicated thing to learn.
They dont work, because not lie detectors at all. To my understanding they're basically just a tech-assisted version of trying to tell if someone is lying by trying to watch their emotional reaction. They might be able to tell you if someone is stressed, under the notion that someone lying will be more stressed than when telling the truth from the effort and worry of being caught, but that isn't really true necessarily.
I wonder why the intelligence agencies (FBI, CIA) still use these to access new recruits π€
Because it lets them see how people react under pressure. If people think the stress detector works, they are more likely to be honest because they are worried the people using it will think they are hiding something. It is a mechinal version of "we already know the truth, we are just asking to see if you lie to us".
The implication of the machine often gets results even though it isn't reliable in any way since stress is not an indication of anything specific.
The most important part of it is βis there anything youβd like to admit, before we take the test?β
Because they get people to admit to things they wouldn't otherwise. A polygraph test starts with the interviewer "just talking" (and those are massive, giant quotation marks there) to you for about a half hour. They slip in little statements about other, experienced officers who are currently employed despite past wrongdoings, "because they admitted" to the bad shit. Meanwhile, when you admit to bad shit, guess who's not getting hired?
The interviewer will give you a giant list to go through, asking if you've done any of the hundreds of bad things, and ask you to explain any "yes" answers you give to the question of committing a crime.
So now you're primed to confess to things, and the interviewer and agency gets to comb through those confessions to see if they don't want to hire you. They also get to reject you if they don't like you and blame it on you failing the 'lie detector' test, or the interviewer can simply say you're lying.
Plausible deniability. The real part of the security clearance is the background check they perform, including the interviews. If they find out from some secret source that you immigrated from North Korea, they won't tell you they figured that out. They'll just tell you that you didn't pass the polygraph and send you home. Your North Korean handler will report back that they need to train future spies how to defeat the polygraph, but fail to close the actual hole in their security.
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They don't. Only shady police that already lie about everything and use it as a tool to lie more effectively
Since the others tackled polygraph's uselessness, I want to comment on another angle:
I think fundamentally in such a case it will be easy for you to convince yourself that you're telling the truth in the moment you say it.
After all you are telling the truth to a version of the question, and you only have an assumption that the questioner means a different version of the question. Even if it's a good assumption, nothing in particular makes your version worse, in fact you could argue it's better.
That combined should make it easy to mentally gloss over the contradiction. So I think your physiological reaction will be indistinguishable from telling the truth on control questions.
Polygraph is basically just there so the interviewer can say the polygraph says you're lying and try to get you to say what that want you to.
Me: Tells the Truth
Interviewer: "You're lying"
Me: "Oh, I'm actually Special Agent [Name Here] on an undercover mission to expose fraudsters pretending to be 'Lie Detector' experts. You're under arrest"
(Actually that's a lie, I'm a sovereign citizen, and I'm performing a citizen's arrest)
Okay you got me. I'm Neptunian.
They're junk pseudoscience as stated in introductory textbooks on psychology & by the National Academy of Sciences & American Psychological Association. Law enforcement keeps them not for their scientific validity, but as an interrogation tactic for people who don't know better.
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That's the neat part: they don't!
βThereβs no unique physiological sign of deception. And thereβs no evidence whatsoever that the things the polygraph measures β heart rate, blood pressure, sweating, and breathing β are linked to whether youβre telling the truth or not,β says Leonard Saxe, a psychologist at Brandeis University whoβs conducted research into polygraphs. In an exhaustive report, the National Research Council concluded, βAlmost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy.β
The real question is, why do people think that they work? Why do government agencies use them to grant clearances when there is no evidence that they can reliably detect falsehoods and ample evidence that they are known to give false positives when people are actually telling the truth?
Go take some classes on stress management and biofeedback and learn to control all those things they are testing for. Then you won't need to worry about what the questioners mean when they ask you something.
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If they make you take a polygraph test, insist on a tarot reading and a full personal horoscope as well. Between the three of them, thereβs no way that they canβt find the truth!
Don't forget to get your Miggs-Bryer personality certificate!
If in the moment you're replying to your own interpretation, you're fine. But the second you overthink about their intentions, you will be freaking out, and that's what the machine sees. One technique for bypassing lie detectors is to raise the baseline by flexing your butthole but there's techniques to catch that, too.
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It depends on how you interpret the question.
Polygraphs "work" by detecting shifts in your breathing, heart rate, perspiration, and sometimes anal sphincter tension.
If you "aren't lying," typically these things do not change (much).
If you "are lying," you'll begin to sweat, your heart rate will jump, and your breathing will become more rapid.
I keep using quotes because all of this is unreliable and manipulatable.
And the anal sphincter thing? That's because usually all it takes to "beat" a polygraph is tightening your butthole.
Edit to actually address your main question- if you were asked "Are you loyal to your country?" and you interpret that to mean "Are you loyal to The State?" and you're not, and you say "Yes," then it would probably pick up on your "lies." But all you have to do is interpret the question in a way that would make you seem "honest."
Oh no, are they going to find my bluetooth communication anal beads?
Nah dude it's a government loyalty test, not a chess championship, calm down
Okay, literally none of these are the ACTUAL answer to the question, and if you're in the US in a position to take a polygraph, I want you to succeed. These people saying that it doesn't work DO NOT MATTER, even if I happen to agree, because you're going to be taking it either way. So, as someone who has actually TAKEN a polygraph with the CIA for a TS Clearance (12 years ago), allow me to tell you the actual answer from my experience:
Before the polygraph is hooked up, you will spend as much time as you need going through every question you will be asked. You have the opportunity to bring up concerns with question ambiguity then. They will work with you to make sure that you feel comfortable answering any question they ask with a straight "yes" or "no". I don't remember what the specific wording was when they asked me that question, and it would technically be illegal for me to tell you anyway. I hope that this is more helpful to you than "hurr-durr, it doesn't work".
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Go read the book called, and I may be remembering this incorrectly, 'Beat the polygraph.' It goes into the history, the failures, and the 'science' of polygraphs. It's enough to get you pretty deep in the subject without reading actual research papers.
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