Lie Detectors Have Error Rates
There are two main reasons why individuals may fail lie detection tests:
The individual is guilty and is lying about the matter under investigation.
The individual is innocent but exhibits reactions similar to those of guilty individuals, as identified through scientific research.
What Does It Mean to “React Similarly” to Guilty Individuals?
In scientific studies, participants are randomly assigned to act as either innocent or guilty subjects. Those assigned as guilty are instructed to commit a mock crime. After committing the simulated crime, they are tested about their involvement, and scientists monitor how their eyes and bodies respond.
The behavior patterns of both guilty and innocent participants are recorded and analyzed. These behavioral patterns are then applied when testing “real” individuals. If someone displays reactions similar to those of guilty participants in research studies, they are classified as deceptive.
Research on eye behavior has shown that guilty participants exhibit significantly different responses compared to innocent ones. Differences include variations in pupil dilation (indicating higher cognitive load), response time to questions, frequency of incorrect responses, blink rate, and reading speed.
Why Might an Innocent Person React Like a Guilty Person During a Lie Detection Test?
There are several possible reasons:
The individual is a victim of a similar crime or behavior, and the test questions trigger strong memories.
The individual is guilty of a different but similar crime or behavior, leading to a reaction to the test questions.
The individual was indirectly involved in the crime or behavior without actually committing the act, such as by helping to plan it, being aware of it and remaining silent, or receiving compensation for not speaking out.
The individual knows who committed the crime and is covering for them, either to protect or assist them.
The individual misinterprets the questions, leading to a reaction.
Can a Guilty Person Answer All Lie Detection Questions Correctly and Still Fail the Test?
Yes, it is possible. Knowing the correct answers to the test questions does not necessarily mean a person is innocent.
For instance, a bank robber might deny robbing a bank by saying “no,” which is the expected response to such a question on a lie detection test. Denying involvement in a crime is the expected behavior.
Lie Detectors Have Error Rates
It is important to note that no lie detector is foolproof. All lie detectors have some degree of error, referred to as error rates.
For example, our polygraph instrument software is 90% accurate, meaning it is 10% inaccurate. This implies that 10% of innocent individuals tested might be classified as deceptive. To understand why this can happen, refer to the first paragraph.
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