Why are polygraphs not allowed in court?

the_silverfoxx

they wont stand in a court of law this is free legal advise ?

coragryph

It is not reliable. And the jury cannot determine its reliability in the same way they can evaluate a witness.

I'm sorry if that's not the answer you want. But that's the real answer.

iritadragon

Polygraphs are only as good as the human interpreting the information. And it is ALL interpretive. I guess the courts decided that there was no way that it could be insured that all polygraph techs got the same training. It was too subjective a science.

Mary S

because they ae not fool proof. polygraphs work by measuring things like heart rate, body temp, and persperation. In other words, they only work if someone gets nervous when they lie. really good liars and pathological liars can beat a lie detecter.

Wilkow Conservative

There is only one reason and that is because they are not accurate. They are so inaccurate I know people who have taken them and it said they lied about there name. A polygraph measure heart rate and brain activity so if you are nervous you will fail no matter how much truth you tell. You can want however many reasons you want to, but the truth is the truth and there is no other reason.

woman38

Polygraphs are rarely admissible in court. New Mexico is the only state in the United States that allows for open admissibility of polygraph exam results. Every other state requires some type of stipulation to be met prior to admitting polygraph exams into record. In most cases, both sides of a legal case have to agree prior to the trial that they will allow polygraphs to be admitted. On the federal level, the admissibility criteria are much more vague and admission typically depends on the approval of the judge.

The main argument over the admissibility of polygraph tests is based on their accuracy.

Often, people who are being given a polygraph exam will employ certain countermeasures in an attempt to beat the instrument. There are Web sites and books that instruct you on how to fool the polygraph. Here are just a few examples of how people try to trick the device:
Sedatives
Antiperspirant on fingertips
Tacks placed in the shoe
Biting tongue, lip or cheek
The idea of countermeasures is to cause (or curtail) a certain reaction that will skew the test's result. A subject may attempt to have the same reaction to every question so that the examiner cannot pick out the deceptive responses. For example, some people will place a tack in their shoe and press their foot down on the tack after each question is asked. The idea is that the physiological response to the tack may overpower the physiological response to the question, causing the response to each question to seem identical.

Many researchers and defense attorneys say the technology is prone to a high number of false results. The scientific reality is far different: The machines measure various physiological changes, including in blood pressure and heart rate, to determine when subjects are getting anxious, based on the idea that deception involves an element of anxiety. But because an emotion such as anxiety can be triggered by many factors other than lying, experts worry that the tests can overlook smooth-talking liars while pointing a finger at innocent people who just happen to be rattled.

It is known that there are false positives, so the real reason is that we believe it is better to save or protect 1 innocent person even if it costs us some guilty ones.

Chris

They are not reliable, can be manipulated, etc. Almost everyone has said that. People have failed polygraphs and evidence has proven them not guilty. A person's emotional state factors into the results, and just because someone is emotional doesn't mean he/she is guilty.

Phil S

They are too unreliable.

hushnowjustplayit

Because they are not a perfect science. People who are unaware of that fact might put too much stock into the results of such a test.

Grist

False positives would happen more often than false witness IDs would.

But the best explanation for what is admissible and what isn't is that all rules of evidence are arbitrary and seldom based on a consistent philosophy of truth and its relation to justice.

yahoohoo

Because they could be wrong.

Big E

Because they're not scientifically reliable. I know people who have lied and passed and others who told the truth and failed. There are just too many variables not the least of which is the subjective interpretation/opinion of the person conducting the test. In Michigan there was just a case where a bank teller was accused of stealing the night deposit. She swore she didn't but failed a polygraph. She lost her court case and was sentenced. A year later the bank found the missing bag! It'd fallen back behind the drop unit!

Earl D

The results can be manipulated intentionally and unintentionally.

If you are nervious while taking an exam it can show false readings.

If you are afraid of the person asking the questions you can give false readings.

If you are good at meditation then you can keep the needle even and solid right after you do the baseline questions.

Obsequious

Yes, witnesses could be wrong, but with a polygraph you're relying on a machine to give you a correst answer, a definite yes or no, from the accussed themself. They can be manipulated in many ways.
I once heard of a man who taped a thumbtack to his big toe & when he answered simple questions like name & address he pressed down on it. Then when he lied he got pretty much the same reaction from the machine without sticking himself with the tack.

katethefabulous

Because they are an imprecise science. You can actually fake a polygraphy. People who are pathological liars can fake it because their body doesn't react when they lie. They are so good at lying that even they believe. The average person probably can't do that, but you can see why you wouldn't want the court to allow a possibly inaccurate polygraph sway a jury's decision. And, if they do it for one, they have to do it for all.

anitababy.brainwash

Well, you've pretty much kicked down all of my reasons.
I don't know what you're looking for. If there was a better reason
somebody's lawyer would have argued it by now. Ya think?

thrill88

While a witness could be wrong, they do have to swear to tell the truth and in most cases the defendant has no control over the witnesses testimony. The defendant, however can sometimes control how they respond to the lie detector, making it possible for the defendant to skew the outcome. Also, if a witness lies they can be held accountable, while a machine can not.

soniaatcalifornia

Well..........For one this is not a proven science in the least. Also the stress analysis is a farce too! The idiot that invented it is not even a legitimate doctor to which he claims he is! There is no way on God's green earth one can truly detect another's lies. It is not a hard proven science in the least. Its just an egomaniacs way of trying to pull one over on someone who they wish to strong-arm into some confession that cannot even be used in court in the first place. Many people are stupid enough to think they are really and truly a fact finding machine when that cannot be further from the truth. If a serial killer can pass it with flying colors what does that say to the general public???????????

chrstnwrtr

Normobrian is correct; they can be manipulated to get flawed results.

albinopolarbear

They are not accurate or reliable. Also, you can train yourself to trick them.

Zelda Hunter

It's becaues they are not reliable, or were not reliable. Professional liars can train to pass them. Jury members are not lie detectors either.

fathead

Defeating the polygraph is a skill that can be learned. It thus has practically no validity as evidence.

You are just ignoring the reason they are not allowed but your arguments are not valid.

leglegl

The rules of evidence require that in order for any scientific evidence to be admitted in court its reliability must be evaluated. This is especially important because jurors may believe that anything "scientific" must be reliable and because a polygraph machine cannot be cross examined. It is my understanding that polygraph tests generally have not been deemed to be reliable enough to be admitted under the guidelines provided by law.

Greg

So that corrupt lawyers can keep their jobs.

Patches6

The polygraph is a tool the police use for intimidation, and to direct them to the actor or actors. According to the police if you fail to submit to a lie detector test for any reason, you are hiding evidence no matter if you are completely innocent and the victim. You are also permitted prior to questioning to see a list of the questions being asked before submitting to lie detector testing.Personally, I feel they are a lot of bunk

Joe-slim

Polygraph technology is a joke. You would get better results from a fortune teller.

symanlegrix

The fact is, they are not considered reliable enough to be considered evidence. From what I've read, its also possible to fool them.

Lee J

Not totally reliable - may accuse people falsely or dismiss guilty people. Based on physiological and psychological reactions that are not universal.

Diane M

As people have said, they can be manipulated. Beyond that, though, juries tend to view them as "science" and to give them more weight than they actually deserve. Think of it as a consequence of the lousy nature of science education in America and the fundamental contempt lawyers feel for anyone who isn't a lawyer.

Cynical? Me? Why, no, I don't think so...

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