Why are polygraphs not allowed in court?

Question

Don't say 'because they could be wrong'. Witnesses could be wrong. Evidence could be wrong. Lot's of things could be wrong. From what I've researched, polygraphs are as accurate as the person giving them.

In a way, jury members are lie detectors. How often is a jury required to figure out who is lying?

There has to be some other reason these are not allowed in court.

Answer 1

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

Answer 2

The polygraph isn't allowed in court because there have been no scientific studies that have validated its usefulness. Known criminals have beat it, and known innocent people have failed it. It has a 10% failure rate even accepting that it is accurate only 90% of the time (some put the figure as low as 70%). This potential for a false positive reading would unduly prejudice a jury because of the nature of the evidence (mechanical).

The reason you can't compare a witness' testimony to a the results of a polygraph is that the polygraph is an instrument, which implies objectivity even before you do a reading. Any time you introduce a machine into court, by implication you are introducing a culturally objective measure of something. This just isn't true with a polygraph.

Answer 3

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.

Answer 4

Actually, it's not so much because they're wrong. It's because they haven't been proved to be right. So many things can change the outcome of a polygraph. Rape victims usually fail polygraphs due to high emotional stress. Physical stress or pain can also change a polygraph results. Age, intelligence, psychological capacity and emotional capacity can all affect a polygraph.
If a polygraph were introduced in court, most jury members would see that as fact, when it actually might not be. Whereas, like you said, jurors get to judge whether or not they believe witnesses and evidence without blindly believing.

Answer 5

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!

Answer 6

I don't know where you got your info from but it did not give you ALL the right info. Lie detector test or polygraphs are NOT allowed in court because they are NOT totally accurate. A pathological liar CAN pass the test EVERY single time he/she takes it. And worse a totally innocent person can fail the same test. This being because a pathological liar doesn't react to the question/s whereas an honest person does. The polygraph is wired and picks up detects senses or nerves. So someone who is taking the test is nervous and reacts and the test does not give totally accurate readings because of this, BUT the pathological liar passes with ease as he/she does not react, so the test does not detect any nervousness.

Answer 7

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.

Answer 8

They're consistently unreliable, and unlike witnesses, the polygraph doesn't have to swear to tell the truth. Also, they require people to not believe in their statements, however, if a person could trick themselves into really believing their story to a point where they thought it was truth, they could easily fool it. The lie detector doesn't do a thorough enough of a job. Witnesses and evidence come under much more scruntiny.

Answer 9

Because they can be manipulated. If the person believes that what they are saying is true, it will show a truthful answer, regardless of the facts.

A false reading would prejudice the jury, and a polygraph cannot be crossexamined like a lying witness.

Answer 10

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???????????

Answer 11

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.