Why do some people fail lie detection tests?
Lie Detectors have Error Rates.
By Russ Warner, Marketing –
There are two reasons why people fail lie detection tests:
- The person is guilty and is lying about the issue under investigation
- The person is innocent but reacted similarly to persons known to be guilty, based on scientific research studies.
What does it mean to “react similarly” to guilty persons?
In scientific research studies, people are randomly assigned to participate as an innocent subject or as a guilty subject. Those who participate as guilty are asked to commit a simulated (mock) crime. After committing that mock crime, they are tested about their involvement during which scientists record how participants’ eyes and bodies react. The patterns of behavior for guilty and innocent participants are recorded and analyzed. Those patterns of behavior are used when testing “real” people. If someone reacts like those who are guilty in a research study, they are categorized as deceptive.
In scientific research studies that looked at eye behaviors, guilty participants showed markedly different behaviors than innocent persons. Differences were observed in pupil dilation (more cognitive load), question response time, incorrect responses, blink rate and reading speed.
Why would an innocent person react in a lie detection test like someone who is guilty?
There are a few reasons:
- The person is a victim of a similar crime or behavior and reacted to test questions because it brought back strong memories.
- The person is guilty of a different, but similar crime or behavior and reacted to the test questions.
- The person was involved indirectly in the crime or behavior but didn’t actually commit the act. They could have helped plan it, knew about it and didn’t say anything, got paid for keeping quiet, etc.
- The person knows who committed the crime and is covering for that person to protect or help them.
- The person misunderstands the questions and reacts to them.
Can a guilty person correctly answer all lie detection test questions and still fail the test?
Yes. Just because someone knows the right answer to a test question doesn’t mean they are innocent. For example, when a bank robber is asked if he robbed a bank, he will likely say “no.” We would expect that person to say “no.” And “no” is the correct or expected response on a lie detection test when asked about bank robbery. Denying participation in a crime is what is expected.
Lie Detectors have Error Rates
Unfortunately, there is no perfect lie detector on the market. All lie detectors make mistakes, which are called error rates.
EyeDetect is 90% accurate. That means it is 10% inaccurate. If a lie detector is 10% inaccurate, then 10% of innocent people tested will be categorized as deceptive. Why would that happen? Refer back to paragraph one.
Photo by / Nathan Cowley
