Polygraph Tests

[stan1980]

What is the general consensus on these? I was watching a trashy UK chat show the other day and they were claiming 99% accuracy. As far as I'm aware, polygraph test results can not be used as evidence in a court room in the UK, but is there any harm in using the results, provided the jury are fully aware on the accuracy or inaccuracy of the results?

There have been high profile cases in the UK where defendants have been prosecuted under very flimsy evidence (Jill Dando case will be familiar to most on these shores), so is there any harm in using polygraph results, when there is already a lot of circumstantial evidence being used anyway to gain convictions?

 

[TooCurious]

I'm not sure of the legal specifics in the UK, but in the United States I'm fairly sure that the reason polygraph results are inadmissible in court is not because of any question of their reliability, but because of the Fifth Amendment, which protects the defendant's right to freedom from self-incrimination.

 

[WatersMoon110]

While I don't know much of the science behind polygraph tests, it is my understanding that they are not allowed as evidence in a court room because they can be inaccurate. I have heard that if someone feels scared or unsure or guilty, then can get a false positive. Also that compulsive liars and people who practice are able to get false negatives. As such, the tests can be fooled and are not good enough for evidence at a trial.

I also don't agree with much of the circumstantial evidence that is allowed in trials.

 

[The Nihilist]

I do not know what rights a defendant has in the United Kingdom, but on our side of the pond, a defendant cannot be forced to incriminate himself.

 

[stan1980]

Yeah, I was talking more about where a polygraph result shows that the defendant is telling the truth and is innocent. Is that admissible in a US court? I'm certain it wouldn't be allowed here, and in a "dodgy" case where the defendant gets prosecuted by the jury, it could be enough to sway a not guilty verdict.

Following on from that question, is a jury fit to make a guilty/not guilty verdict? Or should we use more qualified people to make that decision?

 

[The Nihilist]

http://en.wikipedia.org/wiki/Polygraph#Reliability

 

[stan1980]

http://en.wikipedia.org/wiki/Polygraph#Reliability

Cheers, I had a quick glimpse of that before I started the thread, but there is a dispute with the reliability section.

 

[Bombila]

I've observed polygraph testing to be reliable in one situation, where six people agreed to be tested at the local police station in an effort to find out who was habitually stealing at my workplace. The actual thief volunteeered cheerfully and was apparently confident the polygraph wouldn't work. When it indicated that she was lying, she became hysterical, tried to physically destroy the machine, and began screaming that the devil made her do it. (Really. I hadn't thought anyone ever used that excuse outside of television sitcoms.)

 

[stan1980]

I've observed polygraph testing to be reliable in one situation, where six people agreed to be tested at the local police station in an effort to find out who was habitually stealing at my workplace. The actual thief volunteeered cheerfully and was apparently confident the polygraph wouldn't work. When it indicated that she was lying, she became hysterical, tried to physically destroy the machine, and began screaming that the devil made her do it. (Really. I hadn't thought anyone ever used that excuse outside of television sitcoms.)

When I said I watched a trashy chat show in the OP, I have in fact watched it on more than one occasion (a lot more! ). What can I say, I'm a sucker for cheap TV! Anyway, every time it has shown a person to be lying, the person in question has never disputed the accuracy of the test, which makes me think they might be fairly reliable.

 

[Texas Lynn]

Polygraph tests are an appropriate tool in the investigator's arsenal, but rightfully not admissable in court in and of themselves. They can be used properly to trick a guilty person into confessing but are less useful in clearing an innocent person.

 

[Pogue]

What is the general consensus on these? I was watching a trashy UK chat show the other day and they were claiming 99% accuracy.

Jeremy Kyle?

 

[Texas Lynn]

Once at a police station the polygraph was broken. So a detective went to the cafeteria and got a collander (you know, one of those big strainers for spaghetti and so forth) and put it on the suspect's head. The suspect said "I didn't do it!" and the detective said 'the machine says you're lying' so the guy confessed. The should have just never bothered to have it fixed and just kept on doing that.

 

[Skaloop]

I do not know what rights a defendant has in the United Kingdom, but on our side of the pond, a defendant cannot be forced to incriminate himself.

Which would explain why lie-detectors can't be mandatory, but it does not explain their complete inadmissability. Just as with cross examination, a defendant can answer the question/take the test, or plead the fifth and not answer the question/take the test.