Polygraphs are notorious for being “junk science.” The technology behind them hasn’t been updated since the 1950s, and they are only 80% to 90% accurate.
In fact, some experts say they don’t measure lies. They measure stress. Fear. Anxiety. In fact, the APA would tell you that’s all the machine is. A fear detector. In their report, they said, “There is no evidence that any pattern of physiological reactions is unique to deception. An honest person may be nervous when answering truthfully and a dishonest person may be non-anxious.”
Stress and fear seem to be accurate descriptors for what the average person who has been falsely accused of a crime would normally be feeling when strapped up to an intimidating machine.
There’s lots of evidence that the results depend largely on the biases of the people administering the test, as well as their experience, and skill. For example, test administrators are more likely to “fail” a person of color.
In fact, were you accused of a crime at the state level here in New York you won’t be taking one, because our state bans law enforcement from using them. New York even bans employers from using them. The FBI and other federal law enforcement officials can’t compel anyone to take one, because to do so would be a violation of that person’s 5th Amendment rights.
Even so, federal courts continue to admit polygraph evidence under specific circumstances, usually with the approval of both the defense and the prosecution. A defense lawyer might agree simply because there have been cases where defendants have used polygraph tests to exonerate themselves.
Most often, these are exceptions that prove the rule. In fact, the FBI is aware of the problems with the test. They often use it anyway—as a prop.
The idea is to scare a suspect into believing the machine is accurate. Influenced by this fear, the suspect may confess. It’s essentially the technological equivalent of handing someone a sugar pill to cure their headache.
There’s another problem as well. Even if the results of the polygraph are not admissible in court, the questions asked, and your answers to them, are. This means you could end up making the prosecutor’s case for them.
Even if you’re innocent, and even if you tell the truth.
Why? Because if you’re innocent you don’t know which of the things you’re being asked about actually hurt your case. Details that seem innocuous can be woven together and twisted to create a damaging narrative.
In short, never take the test against your lawyer’s advice. Never take the test without your lawyer present. When in doubt? Don’t take the test at all.