Polygraph and Lie Detection (General)

Polygraph testing is available throughout the United States and overseas. These testing devices are readily available for use all over the world. But why? Simply because liars and dishonest people are readily available, themselves. Polygraph testing is being utilized more often by law enforcement, and even spouses. They are effective in determining if a person is telling the truth about the questions that are specifically asked, most of the time.

There are three approaches to the polygraph test, all unique to themselves.

Polygraph machines are machines that are programmed to measure and record changes in different body responses to particular questions. It is believed that when a person is not being truthful, the heart rate increases, blood pressure will increase, respiration increases and electrical resistance changes. In measuring these changes, a trained professional can determine if the truth is being told, or if a person is having a change in physiological characteristics, suggesting a sign of lying.

The most common among approaches to the polygraph tests is the Control Question Test (CQT).  This particular test can be used in determining if a suspect should actually be prosecuted in connection with a specific crime, or if they were uninvolved in the crime in question. This determination is made by asking a question that the suspect would be truthful about. Some of these honest answers can include their name or their date of birth. From there, a truthful determination response can be identified.  Thus, effectively, giving a guide to truthful and false answers.

The Directed Lie Test (DLT) is used by having a suspect intentionally lie in the answer to a question. The normal types of questions that are asked are, again, usually simple, such as, their name or birth date. From there a lie response is determined and can make it easier when determining the truth from the false information answered. The determination is made by measuring the physiological responses to the questions.

The next approach is the Guilty Knowledge Test (GKT), a multi-choice type question test about a specific crime. One of the answers to these types of questions will be only known by the investigator of the crime. The criminal will answer this and thus provide the test giver that they are guilty. They are generally very case specific questions with incriminating details revealed. This particular approach is somewhat reminiscent of a multiple choice tests that are taken in school, with a verbal answer.

Although this testing is used by many agencies, it is not scientifically sound according to a vast number of psychologists. Of the three approaches to this kind of testing the one that psychologists seem to feel has a sound scientific theory is the Guilty Knowledge Test. Many feel this test can be used as a forensic tool.  

Contrary to popular beliefs, a polygraph test is not a lie detector test. It only measures the changes in respiration rate, blood pressure, heart rate and electrical responses. Many different factors can fool this machine into giving a false report. Some of the little things that can affect the results of the test are anger, embarrassment and nervousness. These can alter your heart rate etc., throwing off the results. But, that’s not all that can toy with the results, having to go to the bathroom, a cold, headache and some medical conditions have also been known to falsify the results and make them appear that the person is being less than truthful.

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