Polygraphs Do Not Work

In an age obsessed with spy-related films, polygraphs appear to be commonplace. But what is truly known about them apart from the ideas planted in our heads by spy movies? Many assume that they all work, and on everyone, unless one is a psychopath. It’s an innocent idea, one in a fictional world where a machine can tell if someone is telling the truth, if they’re who they say they are.

Unfortunately, that fictional world is not the one we all live in, and polygraphs do not always work. So how do polygraphs work? Polygraphs are supposed to work by measuring heart rate, blood pressure, respiration, and skin conductivity, while asking a subject questions. Respiration is measured by pneumographs, which are wrapped around a person’s chest. A blood pressure cuff then measures heart rate and blood pressure. And finally, electrodes, which are put on people’s fingertips, evaluate skin conductivity. There are two types of questions that subjects are asked, the Control Question Test (CQT), and the Guilty Knowledge Test (GKT).

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CQTs consist of ‘control’ questions and ‘relevant’ questions. An example for a relevant question would be, “Did you ever harm a stranger?” if the current investigation involved the subject harming a stranger. The control questions are unspecific, and usually bring to attention a subject’s past. According to the American Psychological Association, an innocent subject would have a larger reaction to a control question than a relevant question, since they know that they did not commit the crime the relevant question was referring to. As for the GKT, it is more like a multiple choice section of the SAT that could get a person thrown in person. Testers will ask questions of which only the guilty would know the answers to.

If the person is guilty, then they should have a larger reaction towards that answer. However, it is also possible that the person simply does not know. For example, if a robber went into a bank, grabbed a load of money, and ran, chances are they wouldn’t know how much they stole. Therefore, a GKT question that refers to the amount of money stolen would be useless. Unfortunately, polygraphs do not work. With all the scientific aspects of the polygraph established, it appears that it would work on everyone.

It has everything, heart rate, blood pressure, skin conductivity, and questions to test a person’s honesty. However, it has one fatal flaw. Is there a pattern that everyone shares that can separate honesty and deception? The American Psychological Association says no. An honest person could be nervous when answering questions, while a guilty one could be completely calm. Another problematic, though beneficial, issue that the polygraph has is that it sometimes acts more as a fear detector than a lie detector.

As George Maschke says, “one can’t have confidence that a person has lied or told the truth based on polygraph chart readings. It’s only really useful when it leads a naive and gullible examinee to make an admission or confession that he or she would not have otherwise made.” Another reason why polygraphs don’t work is because there are ways to cheat it. Many websites online provide tips on how to pass them, and a person was recently sentenced to eight months in prison for telling others how to cheat the system. Antiperspirant sticks that are applied to fingers and palms can prevent a polygraph from successfully using skin conductivity to tell whether a person is lying or not.

Calculating math mentally, biting tongues, and curling toes can also alter the results of a polygraph. Therefore, assuming that polygraphs do essentially work, the results still cannot be trusted. There are real life examples of polygraph tests that failed. Dennis Rader, also known as the BTK killer who murdered ten women, passed a polygraph test, and then confessed when DNA evidence appeared. Gary Ridgeway, another serial killer, passed his polygraph in 1984, before confessing to forty-eight murders twenty years later when police matched his DNA to those found on his victims.

In conclusion, polygraphs do not work, even if media and literature has made it seem like they do. The measuring of blood pressure and heart rate, though scientific, do not give enough insight into the honesty of the subject. Furthermore, past examples of guilty people who have passed polygraphs prove that they are unreliable, and frankly, should not be used.