The lie detector test – also known as the polygraph test – has been around for decades. Soon after it was released onto the market, the validity of the test’s results fell under scrutiny.
A 2003 report by the National Research Council found that there is little evidence to indicate that this test would lead to accurate results. In 1998, the U.S. Supreme Court banned the use of polygraph test results as evidence in many federal courts. This is because such tests cannot provide information about whether someone is lying.
Polygraphs monitor these physiological reactions in the body:
- Blood pressure
- Breathing
- Pulse
- Sweat
Such reactions do not indicate that someone is being untruthful – they indicate that someone is anxious. It is highly likely that anyone facing criminal charges – regardless of their guilt or innocence – would be anxious. Therefore, this test does not say anything of use in a criminal investigation.
Although it is clear that lie detector tests don’t work, they are still regularly used by law enforcement agencies to:
- Interrogate suspects
- Monitor convicted sex offenders on probation
Why would law enforcement bother to use a test that is proven ineffective – especially when such evidence usually cannot be used in court? The answer may surprise you.
Police officers don’t use lie detector tests to seek the truth. They use them to gain psychological power over those being tested.
If the person taking the polygraph test thinks that it is a reliable test of truthfulness, it can give the law enforcement officer the upper hand. If you are sitting in an interrogation room being told that the machine next to you is telling the officer every time you lie, you may be more likely to confess.
A similar strategy applies to convicted sex offenders. As part of your probation, you’ll have to submit to regular polygraph tests and answer questions about your recent activity. If you believe these tests to be effective, it may dissuade you from reoffending.
Ultimately, the lie detector test is itself a lie perpetuated by the law enforcement community. The intent is to make you believe that you can’t hide your secrets. In reality, the scientific community has debunked the idea that lie detector tests are effective. This is why such evidence is almost never used in court.
