How accurate is a polygraph?

[RANCH]

Originally Posted by Kimster

If anyone finds a case where someone's poly showed deception and they were found innocent, be sure to post it here.

Up thread post #13 looks good to me. It's an interesting read.

[TrackerSam]

Originally Posted by HesterMofet

if polygraphs are so accurate, why aren't they allowed in court? Certainly if they were even as accurate as eyewitness testimony (which is notoriously unreliable), they would be allowed as evidence.

The website that is mentioned is a pro-polygraph site. I would like to see independent studies on the accuracy of polygraph testing.

Another issue is that they won't work on true sociopaths/psychopaths who have no guilt over what they have done. If they aren't emotionally heightened or stressed, they won't trip up the polygraph.

Even if I were clean as a whistle, I would never take a polygraph. Way too many variables and chances for things to go wrong.

I hate it when I read on here, "He must be guilty! He refused the polygraph!"
That's just crap.

IMO it's an emotion indicator, not a lie detector. And as one who works in electronics, I would never risk my freedom on any electronic device.

[kgeaux]

Originally Posted by Kimster

"Researchers conducted 12 studies of the validity of field examinations, following 2, 174 field examinations, providing an average accuracy of 98%. Researchers conducted 11 studies involving the reliability of independent analyses of 1,609 sets of charts from field examinations confirmed by independent evidence, providing an average accuracy of 92%. Researchers conducted 41 studies involving the accuracy of 1,787 laboratory simulations of polygraph examinations, producing an average accuracy of 80%."

http://www.polygraph.org/section/res...idity-research

I always believe that "surveys" and "research" done by a particular industry about its particular product will result in biased results. If I am a member of the Polygraphy Industry, and I conduct a study, I would never publish reports that showed the inaccuracy of the polygraph. That would be biting the hand that feeds me, that would contribute to a loss of MY income as a polygrapher. I would only publish the results that tended to support that my business is a sound and good one. So, IMO, any research carried about within the industry is biased at best.

It is interesting to note that this research freely admits that out of each 10 people who are polygraphed, TWO will get results which are NOT ACCURATE. I sure wouldn't want to be one of those two, would you?

Show me some studies done by independent researchers who do not have a financial interest in how the study turns out, and I might be interested.

Every polygrapher brings his own subjective bias into the test......if he has a predisposition to believe a subject is guilty, that is what he will see. When two polygraphers can look at the same results and one will believe the subject passed, and the other will believe the subject failed miserably, well something is wrong. When you add to the mix that the polygrapher can lie to the subject, that even further invalidates the test as a scientific one.

Every Law enforcement officer that I personally know has told me that they would never submit to a polygraph and that they would advice their family members to refuse the test, also. That really says something to me.

[Tilmylastbreath]

I agree. This site says "besides, polygraph doesn't detect lies, it detects changes in the physiology of the body, specifically at stimulus (questions)."

http://www.polygraphplace.com/ubb/No...ML/000219.html

[Mac62]

I read somewhere that M.I.T. did a study on polygraph examinations and found them to be as accurate as tossing a coin. Newer technology may have increased the accuarcy since that study came out, but it all depends on the expertise of the polygrapher.

[Uberfairy]

Polygraphs have improved over the years and can be of help to investigators to entice a confession. Sometimes, after a person has taken a polygraph and told they failed, they will "give it up."
The major difficulty, as I see it, with polygraphs, is the way the questions are worded. They are most effective if they are direct, such as "Did you kill (whoever)?" There was a (bad) show on television for a short time that featured polygraphs as the main way to tell if someone was telling the truth or not. The "contestants" could win money and lose their dignity, marriages,... etc. Clearly the questions were designed in the upper levels of the game so any nagging doubt or guilt would show in the polygraph, even though the person was innocent of the transgression. The show inadvertently depicted how people can fail a polygraph.

But, the end of techniques that deceitful people use is long. All these can throw off a polygraph. Psychopaths can pass them, because they have no conscience, so don't respond with guilt to questions.

However, now there is a new polygraph, called No Lie MRI. An MRI is taken while the subject is asked very clear cut, yes or no type questions. Questions such as, "Did you kill so-and-so?"; "Did you hire someone to kill...?"; or, "Did you shoot...?". I have more faith in these exams, because they do not rely on physical reactions, but on brain wave patterns. When a person creates a story or lies, a different part of the brain is activated. The MRI detects that. This would also be a huge asset for innocent people. Cases have been dropped when the MRI confirmed what the innocent "suspect" maintained.

[Aquaman]

I'm sure many of you watch these true crime shows. How many times have the cops dismissed a person because they passed a polygraph only to find out years later they were guilty? How many times did they pursue innocent people who failed the test?

They have discovered that different parts of your brain are active when you are lying vs. when you're recalling information. I can see the polygraph being phased out as they develop machines to scan your brain during questioning. Of course this won't work on a psychopath.

[Sarah]

How accurate is a polygraph?

I think that really depends how you're defining accuracy.
If the question is "how accurate is a polygraph at detecting the physiological signals that it's programmed to detect?" then with modern technology I'd be inclined to believe the "close to 100%" statistic quoted in the OP.

However, I suspect that the question is really "how accurate is a polygraph at detecting a lie?" and I personally wouldn't put a lot of faith in it.

As I recall, polygraphs are based on the premise that we're all hardwired to tell the truth and lying prompts a subconscious stress reaction which manifests itself through certain physiological changes such as sweating, changes in heart rate and respiration etc.

The problem for me is that there are so many variables to take into account. Some people are more predisposed to showing physiological reactions than others (I know a couple of people who visibly blush when under pressure - absolutely no machine needed there to see what's going on) so the degree of variation in vital signs that indicates stress varies from person to person. It's not an exact science where a deviation from the baseline of x is stressed, y is not stressed and z is indeterminate.

To further muddy the waters, put yourself in the position of an innocent person being wired up to a machine and asked "did you commit this crime?" - I think most of us would show some stress reaction in these circumstances. Ambiguous questions where there's not a straight "yes" or "no" answer can also cause stress while the person makes up his/her mind on what the correct response is.
So even if a respondent shows a definite stress reaction the interpretation of the results is subjective and dependent on the examiner deciding what's a "normal" stress reaction vs a lie and on their phrasing of the questions.

If I was falsely accused of something, it's certainly not something that I'd be willing to stake my future on.

I'll admit to not having read up on it, but in principle I'm not convinced by the MRI method mentioned above either.
I'll accept that it can identify the area of the brain engaged in a complete fabrication but I have my doubts as to whether it could differentiate between recall of a real event and recall of a script / story that had been memorised in advance. IMO that distinction would very likely also be highly subjective.

[mobeydick]

The only way a Polygraph Examination could even be remotely helpfu/usefull is 4 other people besides the target take the test at the same time by the same questioner, graded the passed to 5 examiners who pick out the target independently If they can't the test is useless!