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Are Lie Detectors Valid? Why Can’t They Be Used in Criminal Trials?

Home Forums Personal Security Are Lie Detectors Valid? Why Can’t They Be Used in Criminal Trials?

This topic contains 1 reply, has 2 voices, and was last updated by  joe_r82 7 years, 3 months ago.

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  • #1344 Reply

    Jack Charlie

    I have been thinking a lot recently about lie detectors and lie detection tests. In the not too distant future I am going to be trying to get a government job which will entail security clearance. I will need to undergo a lie detector test. Not that I have anything to hide; I do not. And no, I am not worried about passing the thing, thank you very much. I am just wondering about these machines and tests from more of a conceptual point of view. After all, not many criminal courts allow them to be used as evidence.

    I always wondered that if they are not admissible in court, than why would a company even bother to use them? I guess I am ultimately wondering if a lie detector actually does what most people would assume it was invented to do….namely, catch people who are telling lies.

    Also, since they cannot be used in criminal trials, why not? I mean has their reliability been questioned enough to render them as not strong enough for this level of proof? Or is it simply a question of whether people with enough knowledge can actually ‘beat’ the test itself? Lots of questions. I am hoping to get some decent answers on these.

  • #1345 Reply


    The lie detector is actually a pretty old invention. I think it has been around since something like 1925 or so. The man who developed it was a police officer and figured that when people were lying they would exhibit some physiological changes. The machine was (and still is) designed to measure these changes in things like blood pressure, pulse, respiration and even skin conductivity.

    This is one of the reasons why they start by asking a number of control questions. These are simply used to determine how your body (in regards to the vitals listed above) reacts when asked stupid, ordinary questions. Then, if there are significant changes when they start asking the ‘real’ questions, it is registered as a lie.

    I suppose a business or government agency will use them because they still believe that they work fairly well. However, most scientists do not give much weight or belief to these tests. There are all kinds of claims as to how reliable the tests are, but the bottom line is that the evidence at this point is very inconclusive. This is why they are not admissible in criminal court.

    According to many published papers and studies it is quite possible to ‘beat’ these tests. Some of the methods include making sure to get a lot of rest the night before and go into the test feeling relaxed. Make friends with the person giving the test and make them think that you like them. Other ways are to try and make yourself feel more nervous during the control questions (by thinking about something exciting, nerve wrecking or stimulating), or even pricking yourself with a pin that is hidden. There may even be other ways to beat the test.

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