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Lie detector test/Polypraph

Aquila

Muse
Aquila
Joined
May 30, 2006
Messages
632
I haven't posted for a while but this question has been bothering me for years.I thought that maybe people on this forum could tell me the truth about lie-detector tests, also known as polygraphs.

Does measuring skin conductivity, blood pressure, heart rate or other phsiological changes while hooked up to a machine and answering questions really tell whether a person is lying or not?

So many emotions can effect these measurements, plus some people might be able to control them consciously. I remember when I was studying Experimental Psychology at college, I did an experiment on Biofeedback in which I tested whether people could control skin conductivity if they saw the results visually on an oscillator. Some could.

I just read an article on Yahoo about some football player who had been cleared of drug use based on lie detector. OK, it's only sports. But what about when polygraphs are used in criminal investigations or terrorist trials - do the people who make laws and govern this country really believe in them? What is going on? I don't know if this has been discussed before on this forum, but if it has perhaps you could direct me to the thread.

Thanks.
 
Unless you're REALLY good...your body responds differently when you lie.

I'm trying to find the article that explains how everything works.
 
Azure said:
Unless you're REALLY good...your body responds differently when you lie.
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Yes, but your body also responds "differently" when you have indigestion or are worried about your mortgage. There is nothing that links (scientifically - objectivly and with proof) skin-conductivity with lyring. The test seems to have no scientific basis!

And what does differently mean? Differently from what? Is there some sort of normal reading, for the average person?
 
Are there correlations between physiological changes and consciously fabricating information? Yes. But it is far from a simple situation.

First of all, while many people share some of the physiological reactions, getting it to be wholy reliable is far from easy. False positives and false negatives abound due to variations in reaction. Versions in the past have been easy to circumvent by artificially inducing certain reactions to read like the 'zero' or 'baseline' readings (for instance, if your heart rate is excited on the zero reading, it can't be used to indicate a lie if it excites in reaction to a particular question).

Secondly, a lie is only detectable if your physiology reacts to the statement you're making. In other words, if you truly know you're making it up. If this is not entirely true (you might be mistaken or less than confident, but still feel you've got elements of truth in it), then it won't be detected.

Polygraphs are inadmissable as evidence for a reason. The greatest crime is when it's used on those horrid talk shows to 'reveal' some girl or guy has been cheating, or doing the dirty.

Athon
 
It's fairly worthless. Under optimal conditions supporters claim 70% accuracy, which is pretty worthless. Interpretation is subjective. It's main use is to intimidate people into confessing. There are many easy ways to beat it.

The "normal" reading comes from a preliminary setup where they ask people to tell the truth and to lie.

If you want to read a 220 page e-book, you can see everything you want to know.

Somewhere online there is a mathematical analysis of the 70% accuracy claim--I couldn't find it, but I bet if you read all the links in this Skepdic article you will find it.
 
Polygraph tests -- Science, Quackery, or Intimidation?

The polygraph equipment measures heart rate, breathing rate and depth, and skin conductivity. All these are valid measurements, and it takes a person to interpret their meaning ... just like the Scientologists, the Psychics, and quite a few Chiropractics and Homeopaths do.

I am not saying that polygraph examinations have no validity at all.

I am saying that they are used mainly to intimidate a suspect into confessing. I know, because I've been through one (only one -- see disclaimer below).

The examiner kept asking "When did you do it?", "Why did you do it?", and "Who did you do it with?" for 30 minutes after I had said "No" to "Did you do it?"

Then the examination was called off when it was reported that the real perp had been pulled over with a car full of evidence. Even then, the examiner kept insisting that I'd had something to do with the crimes, while making contradictory excuses as to why his interpretations did not match the facts. The prosecutor/D.A./whoever didn't even try to bring charges against me. My guess is that the examiner had something to prove, and I just happened be available.

All told, there was no material evidence whatsoever to connect me to the thefts (I didn't do it -- I was in another state at the time, with witnesses), yet the examiner tried to intimidate me into making a false "confession."

Disclaimer: Of course, this was over 30 years ago, and with the technology of that era. I was 20 years old then, and it happened to me only once.

Polygraph tests -- Science, Quackery, or Intimidation?

All of the above?
 
The use of pseudo-science and quackery in the form of polygraphs by the police, FBI and CIA doesn't create a very good impression of America for the rest of the world. It makes us look like a bunch of controling thugs. Not to mention our reputation in science and education.

I wish that James Randi and skeptics in general would spend less time on debunking psychics who just do what they do for entertainment or because people want them to, and more time debunking the use of polygraphs by government agencies, which is a serious breach of integrity for everyone concerned.
 
I haven't seen any studies, but I can speak from personal experience...

I had to pass a poly to get my current job. Just a general poly about my life, drug use, and trustworthiness. I had nothing to hide, but was still nervous! :blush:

The examiner did the calibration (telling me to tell the truth, then to lie) and we started on the questions. One of the questions was "have you ever betrayed someone who trusted you?" When I answered that question on the form months before, I hadn't thought anything of it. Sitting in that chair with my mind racing, I remembered I had cheated on my girlfriend many years before. :o

When we got through the first round of questions (the test involved going through the same set 3 times), the examiner came around and said he'd noticed a strange reading on that question. I told him what I was thinking. He asked if that was the only thing and I told him it was. He told me that wasn't a major deal and went back to the machine. The next two times through, there was no reaction to that question.

Granted, I am a rather honest and upfront person, so I've never learned to hide a lie. So maybe I reacted strongly because I had no defense against it. All I know is that the machine DID pick up on my one evasive answer, and when I was told I was OK, it didn't pick up anything.
 
ChristineR said:
It's fairly worthless. Under optimal conditions supporters claim 70% accuracy, which is pretty worthless. Interpretation is subjective. It's main use is to intimidate people into confessing.
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This reminds me of a story I heard. (Not sure where though.... could be in one of the books I read on criminal profiling, but I could be wrong.)

Some cops hooked a suspect up to a 'lie detector', except that it was really a photocopy machine. All the copier had was a sheet of paper that said "He's lying". So, whenever the suspect answered a question that the cops thought was wrong, they'd hit the copy button, and the suspect would be confronted with a sheet of paper "proving" he was lying.
 
I have taken two polygraph tests and both times lied more then once during the exams. I passed both with no problems. The techniques they used were just like I had researched before hand. Such as picking a card at the beginning of the test and having the examiner show how he can determine which card is mine, thereby showing how easily he can spot me lying. I found the whole process a joke, but I can see how someone who doesn't know anything about the tests and thinks they are real can be intimidated.
 
There's an article about polygraphs on UK Skeptics. Basically, as others have already said, they cannot detect lies. What they can do however, is intimidate people into telling the truth. The operator knows full well that the device is useless, but as long as the person being tested believes it works then they are more likely to tell the truth to start with. It's just another psychological tool for interogations, nothing more.
 
IlikeFrogs, if you the 220 page document you will see that the polygraph operator expected you to lie on the "Have you ever betrayed anyone you trust?" question and falsely implied that it might be a problem if you had done so.

This is called a control question, and provides the baseline which others statements are compared against.
 
Buckaroo said:
Polygraph tests are a sham. The results are obtained through the use of psychology (read: intimidation) and outright lying on the part of the examiner -- the machine itself is just a prop.
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And yet lie-detectors are still talked about on the local and national news as though they were scientific.

Please could we have someone like Bill Nye, or another respected advocate of science education publicly address this issue on T.V. or in the printed media, so that every citizen of this supposedly free country can understand it once and for all. It is a national disgrace.
 
Cuddles said:
There's an article about polygraphs on UK Skeptics. Basically, as others have already said, they cannot detect lies. What they can do however, is intimidate people into telling the truth. The operator knows full well that the device is useless, but as long as the person being tested believes it works then they are more likely to tell the truth to start with. It's just another psychological tool for interogations, nothing more.
Click to expand...

Yes, I remember reading an article about polygraphs in which the author summed it up nicely by saying that if the subject thinks they will work, they work; if the subject thinks they don't work, they don't.
 
I once saw an episode of Dr. Phil (shut up) where they polygraphed some schlub. The polygraph operator kept claiming a '90% accuracy rate' (heck, it might even have been 99%), and all I could think was how on earth do they even calculate that? Seriously, how does a polygraph operator even know their own accuracy level? After the test, ask the subject 'hey, can you fill out this form indicating when you were lying and when you weren't so I can determine how accurate I was?'
 
I've been in law enforcement a long time (1968) and my opinion is that the "accuracy" of the lie detector is entirely determined by the operator. Essentially, the general public believes that the thing can detect lying, and a skilled and perceptive operator (who would make a good interrogator without the machine), manipulates that belief.

60 Minutes did a nice little test some years back, setting up a phony camera shop and "employees". They hired three different private lie-detector firms to question the employees about ongoing theft. They also made it known to the operators that they suspected so-and-so.
In all cases, the operators found the suspected employee "guilty", even though the entire thing was fictional.

Despite the heavy use by law enforcement, no court will accept the tests as reliable.
The latest thing is the "voice-stress analysis" test. I have heard investigators intimidate suspects with lines like "it's 100% reliable".
Nonsense, of course, these things have been around for many years; I recall when the technology became available, and testers were "examining" the recorded statements of all sorts of political figures....
 
I like how some operators ask if you are on any medications. As if they really are able to calibrate the machine for every medication and combination of medications. The whole thing is too subjective to be accurate enough to be used as evidence.

The FBI and CIA have been widely testing their employees for decades and there has never been a case of a spy being caught through polygraph testing.
 
But they use it on Maury! How can it not be true!

I remember in the Haggard affair the polygraph displayed a false positive. So either gays render it defective, or it is not accurate.
 
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