Polygraph Exams
Can It Really Detect Lies?
By Daniel Muniz

The scientific community has never been convinced of the validity of polygraph exams. There are quite a few reasons why science has been doubtful but long story short is that lie detector tests don’t really work and that has been the basis for the skepticism. And this resistance as well as opposition from civil liberties groups has helped prevent the results of polygraph exams from being admissible as evidence in most courts.

So what is it about lie detector tests that make them scientifically unsound? And if the test results are totally useless for a trial, then why do law enforcement and so many governmental agencies make such extensive use of them?

The instrumentation of the polygraph machine monitors the physiological variances of blood pressure, heartbeat, galvanic skin response, and respiration when the subject is given a series of questions about a set of events. The purpose is that a deviation from an established baseline of truthfully answered questions would represent a lie. So in other words, any response that is outside of truthfulness would produce a measurable physiological variance and a trained tester would be able to detect it.

That is an interesting theory but does it work?

The scientific community says no. And the rationale is that just about anything under the sun can produce a physiological variance which does not necessarily mean that someone is lying.

First, take a look at some of the basic human emotions such as fear, anger, rage, anxiety, embarrassment, sadness, etc. During questioning, any emotive state can cause a shift in a person’s physiology and its intensity can amplify the deviation from the baseline. For example, suppose someone is nervous about taking the test and a certain bold question spikes that nervousness which causes a variance in breathing like a gasp of air. As a result, someone’s emotional state may have absolutely nothing to do with lying but the variance can be interpreted as such.

Next, take a look at some of the basic human physical conditions. A headache or a cold or any other sickness can cause the deviation at any time because the body is reacting to the illness. And what about passing gas (or trying to hold it), constipation, or needing to take a quick (or a very long) trip to the bathroom. There are just so many temporary and involuntary physical states that may be completely hidden from the tester.

In essence, it is not possible to account for every emotional and physical state and then accurately correlate the right ones to lying. But it is this correlation that makes a lie detector so dubious as a forensic tool. Quite a number of tightly controlled scientific experiments have vividly demonstrated how unreliable the polygraph exam really is. And sadly, there are too many real life examples that have attested to its weaknesses such as traitor and spy Aldrich Ames who compromised our national security while working for the CIA even though he frequently passed the lie detector test.

So if the polygraph exam can be voluntarily or involuntarily manipulated, then why is there still so much widespread use especially amongst law enforcement?

Interestingly, many in law enforcement who are the most ardent supporters of using lie detector tests on suspects are reluctant to voluntarily submit to a test. They know full well that the polygraph exam is bogus but more often than not, the suspect doesn’t know that and it is this ignorance that can be fully exploited.

For example, a violent thug who never graduated high school gets strapped to a futuristic high tech machine that looks like something right out of Star Wars. In the pre-examination interview, which is actually a covert but legal form of interrogation, the technician spouts off all of the wildly untrue scientific claims from the manufacturer about how accurate and reliable this state-of-the-art contraption from Buck Rogers really is. If the technician is convincing enough to explain how foolproof the test is, a suspect may break down and confess to the crime even before the exam begins.

If not, there is still a good chance of the suspect making a confession during the post-interview when he or she is harshly confronted with the test results.

Accordingly, perception becomes reality to the uninitiated. In summary, the polygraph exam is not a forensic tool inasmuch as it is useful in the art of deception to trick a legal confession from a suspect.

Now I am not necessarily opposed to law enforcement using such means because a confession is still voluntary and it is an effective way to put some dirt bags behind bars. The problem I have is when the police use the polygraph exam as their only tool instead of relying on hard evidence and real detective work. If it is abused in this way, a false confession can be extracted from the wrong people or the results can be used a means of harassment. Unfortunately, an easy person to convict is someone who is innocent and naïve.

Likewise, employers use the polygraph exam as a deterrent. It is simply a tool to scare off the people who really shouldn’t be there in the first place. But as many governmental agencies have learned the hard way, the lie detector test is totally worthless as an effective safeguard.

Overall, it is disheartening that a fraudulent technology is being used at all because it is nothing more than an expensive hoax. The only reason it has any value at all is because we have an unsuspecting public that doesn’t know any better.

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