How can polygraphs possibly be accurate?

[Seegtease]

So, I was watching some youtube videos of the game show "A Moment of Truth" which seems like it's pretty much staged, but whatever. It got me thinking about lie detectors.

I know it has something to do with pulse rate and maybe blood pressure, or something, when you're lying, and some signals from the brain. How can this possibly be accurate? How do they KNOW it's accurate? Sure, there's solid stuff you can test like name, age, weight, height and so on, but for questions like "have you ever cheated on your spouse?", how do they verify whether or not the machine is accurate? One might argue that they don't need to because they can ask the verifiable questions to test the integrity of the machine, but usually those kinds of questions offer no real pressure on the test taker.

If I were taking a lie detector test (on that game show) and it asked me something incriminating, even if I were innocent, I know my heart rate would jump and other signs of nervousness or tension would show up because I'd be worried that the machine would falsely detect! So then, my worry would in turn cause the machine to give a false reading of a lie.

How can one accurately test the integrity of a lie detector, and even if they do, how can they be 97% (or whatever the number is) sure that it is accurate the same way on ALL people?

One of the questions was "do you think you're a good person?" and she answered "yes" (right after admitting to many incriminating things, so you know she has no reason to lie about this kind of question), and it buzzed as a lie, meaning she does not consider herself a good person.

Being that she'd have absolutely NO reason to lie on that (right after admitting to adultery), I can only conclude that the machine is wrong. Doesn't make sense.

[sinisterwyvern]

That's the thing, they start the test by asking mundane questions like your name or like gender that you will answer truthfully and gain a "baseline" to which the machine then measures against.

[evoco]

They're not. As for how they know people are lying, it's not that they KNOW they're lying, they rely on control questions and then contrast to the answers, if there is a large physiological difference they are assumed to be lying.

Polygraphs are not all that accurate - they can be beat, and they can give false positives depending on the individual being tested. Also the polygraph test is only as good as the analyst interpreting the results. Do they work sometimes, yes, but not enough for it to be taken as fact. It's part of the reason they are not generally admissible in court.

[Deleted]

If I were taking a lie detector test (on that game show) and it asked me something incriminating, even if I were innocent, I know my heart rate would jump and other signs of nervousness or tension would show up because I'd be worried that the machine would falsely detect! So then, my worry would in turn cause the machine to give a false reading of a lie.

Was thinking this exactly. If I was asked like, have you ever commited a crime, I know my heart rate would jump up because I would think like fuck, even tho I've never commited a crime. Please gif explanation!

[Deleted]

They can't be accurate, it's why they are inadmissable in a court of law,

[vizzle]

I've always wanted to take a polygraph exam to see if I could beat it. I think if you just prepared yourself mentally for every possible question they could ask (did you fuck the president's wife while you assassinated Elvis Presley?) then you could just be relaxed and they wouldn't see anything wrong.

[MortalWombat]

Well I'm just going to go with the theory that the thing itself isn't real and it's just there so you don't find out about the mind reading alien they have behind the glass. Seriously though I would probably try to make myself as calm as possible and give them the dumbest answers to their questions that I could think of to see if the thing reacted or not.

[Stuffs]

They arent accurate. Theyre notorious for being wrong, as well as being tricked with practice.
People just like pretending they are because they watch too much CSI or something

[haxartus]

They aren't accurate.
They don't measure if you are lying or not, they measure how excited are you about the question. Which doesn't necessary indicate lying.

[evoco]

They can't be accurate, it's why they are inadmissable in a court of law,

They're not inadmissible in all courts. Only 23 states have banned polygraph evidence, and New Mexico full out allows it.

[Julian Rayne]

Polygraphs are about 10% more accurate than flipping a coin. It's a load of Tauren.

[Seegtease]

That's the thing, they start the test by asking mundane questions like your name or like gender that you will answer truthfully and gain a "baseline" to which the machine then measures against.

Except it's a totally inaccurate baseline because my physical reaction to "how old are you?" varies greatly from my reaction to "have you ever cheated on your spouse?", no matter what my answer would be.

They can't be accurate, it's why they are inadmissable in a court of law,

Well, people sure do seem to put a lot of stock in them, especially in this particular game show. People are stunned by the answers, while the first thing I'd think isn't "SCANDALOUS" (as the masses seem to) but more like "lol polygraph".

---------- Post added 2011-11-27 at 02:16 AM ----------

They aren't accurate.
They don't measure if you are lying or not, they measure how excited are you about the question. Which doesn't necessary indicate lying.

Do you want a free ticket to Disneyland?

Yes!! *BUZZ*

[Deleted]

I've always wanted to take a polygraph exam to see if I could beat it. I think if you just prepared yourself mentally for every possible question they could ask (did you fuck the president's wife while you assassinated Elvis Presley?) then you could just be relaxed and they wouldn't see anything wrong.

Their the Illuminati bro, they will find out ANYTHING. Even if you're prepared, they will ask like "Did you have a relationship with the goat you had when you were 5?". And you'll be like "WTF?!" and your heartrate will raise.

[Wells]

Except it's a totally inaccurate baseline because my physical reaction to "how old are you?" varies greatly from my reaction to "have you ever cheated on your spouse?", no matter what my answer would be.

Thats the point.

They're not inadmissible in court because they're inaccurate, they're inaccurate because they're circumstantial.

[haxartus]

Another thing is that if you are a criminal and believe that the polygraph is accurate, you might be concerned about the possibility of being caught, which will show on the polygraph.
However, if you are innocent and believe that polygraphs are inaccurate, you might be concerned about the possibility of the polygraph falsely accusing you, which will show on the polygraph.
There is no real way to tell the difference between these two.

[Yseraboy]

They're not inadmissible in all courts. Only 23 states have banned polygraph evidence, and New Mexico full out allows it.

But they can only use it against you if you agree to take it in the first place.

My father was in law enforcement, and he didn't like polygraphs for one reason: they are a win-win situation for the defense.

1. Test shows you are lying: claim the test is flawed, "junk science" = reasonable doubt = win
2. Test shows you are telling the truth: proclaim that the test indisputably exonerates you = reasonable doubt = win

[evoco]

But they can only use it against you if you agree to take it in the first place.

My father was in law enforcement, and he didn't like polygraphs for one reason: they are a win-win situation for the defense.

1. Test shows you are lying: claim the test is flawed, "junk science" = reasonable doubt = win
2. Test shows you are telling the truth: proclaim that the test indisputably exonerates you = reasonable doubt = win

Can't dispute that lol. As for taking them, people are dumb and agree to things they shouldn't.

[Auloria]

Polygraphs are about 10% more accurate than flipping a coin. It's a load of Tauren.

That sums it up nicely. They are well-known to be worthless, and can easily be beaten.