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On TV and in movies, polygraph tests or lie detectors are a popular way to nail a suspect. But are they actually admissible in court?
Courts don't have to admit lie detector tests, according to a U.S. Supreme Court case that specifies how courts deal with scientific evidence. Instead, individual judges have discretion to decide if a polygraph will be admitted based on certain criteria.
Why isn't it a clear yes or no, as to whether lie detector tests are admissible? To get to the answer, you need to know a bit about how lie detectors work and how courts deal with scientific tests.
Polygraph tests are based on the assumption that people give off certain physiological indicators when they lie. That includes things like increased heart rate and perspiration.
The polygraph machine is hooked up to a suspect and measures a variety of factors to determine if someone is lying. Lie detectors were very popular with law enforcement for years, but now their findings are often questioned.
The problem is that polygraphs can be fooled.
In some cases, people intentionally fool them by practicing telling a lie so that their body doesn't betray them during the test. Those kinds of countermeasures can prevent the machine from getting an accurate readout.
There's also a less devious and interesting way to fool a polygraph test. If you're nervous while the questions are being asked, the results will likely be inconclusive.
It turns out the symptoms of nervousness or anxiety are the same symptoms people exhibit when lying. So for individuals who are worried about the test itself, it may be hard to distinguish that fear from the reaction produced by actual lying.
Because of that kind of inconsistency, the Supreme Court instituted standards for determining if scientific evidence, like a polygraph, could be admitted in court.
For something like a polygraph test, the party that wants it admitted must show that the theory behind it was tested and subject to peer review and publication. The test must also have a known error rate, and it must be generally accepted by the scientific community.
In some cases, like in military courts, the use of polygraphs has been banned outright. But generally speaking, it's an individual judge's decision. Each judge must make an evaluation based on the information provided, and so each court can decide differently.
That doesn't mean a lie detector is something to laugh about. But understanding how it works may make you more comfortable and thus less likely to get a false positive.
Even if the test isn't used in court, it can still be used by police during questioning. If that happens to you, make sure to have an experienced criminal lawyer present to make sure there's no funny business.