Do Lie Detector Tests Actually Work? [Debunking Myth]

Lie detectors tests are a fantasy of science-fiction writers. Wait, what? What about lie detector tests used to catch criminals? I ask which criminal? Unlike time travel, people actually believe that they are real. And, this misunderstanding stems from the way these tests are done.

I am not claiming that lie detection tests don’t work. However, they don’t detect if a person is lying. They cannot. No test can.

History of Polygraph Tests

The first unofficial polygraph test was made around 100 years back by a Californian policeman John Larson (1921). He studied the variation in examinee’s blood pressure in comparison to when they spoke the truth and when they lied. It was welcomed warmly by his fellow policemen—but the court rejected it when they presented it as a piece of evidence—as it did not get enough recognition from the experts of the respective field. Neither that time nor now, it got validation from scientists. It is malarkey.

How Does a Polygraph Test Work?

During a polygraph test, the subject (accused/examinee) is submerged in a confined place with a polygraph tester (examiner). You will be surprised to know that you don’t need a lot of scientific knowledge to become a polygraph examiner. You need to be a crime specialist where a degree in psychology is a plus point. Along with that, you need to undertake the training of mere 9 weeks.

A so-called lie detection test constitutes two types of tests. Comparative question test (CQT) and Concealed Question test (CQT).

What Is a Comparative Question Test (Cqt)?

A comparative question test contains series relevant questions and irrelevant questions. A relevant question is any question that is related to the subject of investigation. For example, if a thief is being tested, we would ask questions like “Where were you when the robbery took place?”. Whereas, an irrelevant question is completely unrelated to the investigation. It could be simply “What month of the year is this?”.

The examiner then studies how the examinee reacts when they asked a relevant question in comparison to an irrelevant question. It is expected that an innocent examinee will panic when asked both relevant and irrelevant questions. He will behave the same way. Whereas, only relevant question will affect a culprit.

What Is a Concealed Question Test (Cqt)

A concealed question test contains a question with different options out of which one is correct. For example, it could be “From where did you break into the house—the terrace, the backdoor, or the backyard?”. The examiner then changes the sequence of the options provided. He could say the correct option first followed by the remaining incorrect options.

Also Read: ← How Math Is Helping Us to Reduce Crimes

After asking these questions with variant combination of options, the examiner studies how the examinee reacted to each of the options given to him. It is expected that the innocent will answer all the questions—irrespective of the sequence of the options—in the similar fashion. The culprit will show suspicious behaviour when he will hear the correct option.

What Does Polygraph Test Measure?

A polygraph test measures three things:

  • Cardiovascular variations: The beating of heart. The flow of blood in and out of an examinee’s heart during the examination.
  • Respiratory variations and pulse rate: The pulse rate. The flow of air in and out of his lungs
  • Electrodermal Variations: The skin conductance. When we are aroused, afraid, or excited, our skin holds stronger conductance to electricity. The clip on the finger measures the sweat dripping from it.

Why Does It Not Determine Honesty/Dishonesty?


  • Fear: When an examinee’s heart beat increases – let’s say more than 100 beats per minute – while answering a question, there is no way to know if it is because he is lying or he is scared. Perhaps, the examinee is innocent and finding himself with such an accusation and being examined in such a way, his pain-body (that Eckhart Tolle talks about in The Power of Now) activates. In fact, many people will be naturally scared even if you verbally accuse them for stealing a pen. It could be because they have social anxiety or had some bad experience in the past.

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  • Escape: While an innocent can be mistakenly proven guilty, a culprit can escape. A person whose hands didn’t shake while slaughtering someone’s neck will stay cold and confident when you will ask him if he did so. In case of serial killers and psychopaths, there are even more chances that they will feign their behaviour—portrayed as an innocent person—since they are less emotionally stimulative.
  • Lack of evidence: Polygraph test is neither proven through theory nor data. In fact, several social experiments made showed that there were inherent inaccuracies in the polygraph tests.

(PDF) The pseudo-science of “lie detection”

  • Placebo Effect: In general, a polygraph test’s results are largely dependent on the placebo affect. If the examinee believes in the accuracy of the polygraph tests, they are likely to panic. Where the candidates who didn’t have any prior fear of it will pass by.
  • The Examiner: You cannot escape bias during a polygraph test.


There is barely any. Actually, there is one. Polygraph test is a part of pseudo-science—it’s a swindle.

Additional Resource:

You can download a polygraph software and play it yourself from here.

Ahmad Khan

I have no blood in my veins. I have ink.

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