Why can't they just use lie detectors in court?

Question

To see if the person is innocent or guilty or something leading up to the final decision, why can't they use lie detectors?

Answer 1

I find it very interesting that the majority of these answers state that since lie detectors are not 100% accurate that is why they are not used in court. Most testimony in court is FAR from 100% accurate, especially eyewitness testimony, yet we use it routinely and juries rely on it disporortionately to other more objective testimony and there is no outcry about its well researched and documented inaccuracies. So it is NOT merely the accuracy level of "lie detectors" that keep them out of court. As a matter of fact, polygraph tests are NOT always disallowed in court. That is up to each jurisdiction and the circumstances surrounding their use. Personally, I would rather rely on a well-administered polygraph by a certified and trained examiner than an eyewitness any day. If people actually STUDIED polygraph testing instead of relying simply on what they are told about them, I think they would agree.

The true answer is it has much more to do with the right against self incrimination than the accuracy of the test.

Answer 2

If you tense your muscles, it can send alot of readings haywire in the detector. The lie detector is designed to test heart rate, stress level, pitches in your voice (if they change to a higher pitch or lower pitch it may detect that your lieing), brain patterns.

It is not at all accurate and could put someone away for life just because they had a twitch, or are under pressure with the lawyer yelling in their face for an answer.

Answer 3

the optimal issue with a lie detector is that there is adequate doubt of their ability to easily hit upon lies. despite if a lie detector could be shown scientifically to be ninety 8% precise (which might look fantastically reliable), there continues to be a genuine looking probability that it is not precise. This creates genuine looking doubt interior the instruments ability to hit upon a lie. In maximum courts, lie detector info is inadmissible because of this volume of genuine looking doubt.

Answer 4

Lie detector tests are not accurate when it comes to measuring truth and deception. They are accurate when measuring respiration and perspiration. They do not measure whether or not someone is lying, they measure how the body reacts to certain questions and answers. They are tests whose results rely on the subjective interpretation of someone who may not be independent.

At best, lie detectors can be offered as circumstantial evidence which, along with other evidence that proves nothing but suggests everything, can be used against a defendant in some circumstances.

Oh, and to the poster below, I *have* studied the evidence for and against polygraphs. They measure physiological data. Although many people's bodies can react in certain ways when lying, there is no conclusive connection between lying and physiological reaction.

Answer 5

lie detectors are not 100% accurate - far from it. since court (in the US) involves "innocent till proven guilty" and the guilt must be "beyond a reasonable doubt," if there is a doubt in the accuracy of the lie detector, then it cannot be used to say one is guilty - or innocent.

Answer 6

Because lie detectors aren't anywhere near 100% accurate, but the average person thinks they are.

Answer 7

Because they are not reliable.

All a lie detector does is detect stress - it cannot really detect a lie.

Answer 8

That's not their purpose. They measure stress levels, and if you've ever been in court, you would know there is nothing but stress in there, guilty or not. It would also slow everything down even more.

Answer 9

Lie detectors are innacurate

Answer 10

lie detectors aren't reliable. there are alot of ways to cheat, and control your heartrate