Various cultures have searched for ways to accurately detect lies at different times and ages in human history. Polygraph tests have emerged as a tool to detect deception in diverse fields such as national security, police investigations, company recruitment, and employee theft.
In this article, we’ll explore the history of polygraph testing, how a lie detector test works, the validity of polygraph exams, and more.
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History of Polygraph Tests
A policeman and physiologist, John Larson, created the first polygraph in 1921 when he created an instrument that measured changes in the heart rate, respiration rate, and blood pressure. However, his work was influenced by William Marston and Vittorio Benussi.
Later in 1923, Marston attempted to have the polygraph test results used as evidence in United States v. Frye, but was rejected. However, Larson’s protege, Leonarde Keeler, continued working on the polygraph, and in 1935, it was used to convict two suspects in Portage, Wisconsin.
Initially, the data collected during a polygraph test was recorded using analog instruments. Then, the data would be printed out on a moving sheet of paper with several pens moving to report the data.
Due to this process, the record of an individual’s responses during the actual polygraph test is called a polygraph chart. However, most polygraph tests today use computerized recording systems to collect the data.
What Is a Polygraph Test?
First of all, what is a polygraph, and how does it work? A polygraph examination is also known as a lie detector. It is an instrument that measures involuntary physiological changes in blood pressure, heartbeat, respiration, and perspiration — reactions allegedly linked with the anxiety caused by lying — while a subject is asked questions.
A lie detector uses a device or procedure that measures several physiological indicators such as blood pressure, pulse, and respiration. A person is asked a series of questions. Lying is associated with increased breathing rate, elevated heart rate, higher blood pressure, and an increase in perspiration or sweating.
The polygraph records the individual’s physiological response to relevant questions. The polygraph examiner now reviews the person’s physiological response to the questions to assess if the person is telling the truth. Polygraph tests are often used in investigating crimes.
How Does Polygraph Testing Work?
The polygraph is an instrument with sensors attached to the individual taking the test. These sensors range from four to six, depending on the type of machine. The sensors record a person’s breathing rate, pulse (heart rate), blood pressure, and perspiration. The measurement of these areas is called physiological responses.
Breathing rate is typically measured by a pneumograph, a coil wrapped around a person’s chest that measures the frequency and intensity of a person’s respiration. Heart rate and blood pressure are calculated by using a blood pressure cuff.
Electrodes are connected to a person’s fingers to measure perspiration or electrodermal response. These electrodes can be disposable or small metal plates. This measures changes in skin conductivity caused by electrolytes found in sweat.
The theory behind lie detector tests is that lying causes anxiety and this leads to involuntary physiological changes like a faster heart rate, etc. A polygraph examination begins with control questions to gauge these physiological reactions when a suspect is answering truthfully. A significant change in measurements in response to relevant questions could suggest the person is lying.
What Happens in a Polygraph Examination?
A polygraph examination has different phases. The first is a pretest phase, where the paperwork to administer the test gets completed. The examiner also explains the polygraph test process and answers any questions the individual taking the test may have.
The questions used for the actual exam are also reviewed during this phase to ensure understanding. When the polygraph test starts, the questioner asks three or four simple questions to establish the norms for the person’s signals. These control questions provide a baseline for when a person is answering truthfully.
The next is referred to as the chart collection phase. The examiner administers questions and collects several polygraph charts during this stage. The number of questions asked and the charts collected varies by case.
The final stage is the data analysis phase. During this stage, the information collected through questioning is reviewed and analyzed. The examiner, at this point, decides whether or not deception was present. At this time, the polygraph examiner will give the individual being tested an opportunity to explain their responses to some of the questions when needed.
How Accurate Are Polygraph Tests?
Polygraph testing is estimated to be 87 percent accurate. Polygraph results can be inclusive and may give false positives. An innocent person may fail because of nervousness and other factors like drug use can cause the same physiological responses to the fear of being caught lying.
Is Polygraph Evidence Admissible in Court?
Polygraph test results are generally not admissible in court. However, there are some exceptions such as when both parties agree to allow polygraph evidence to be admitted. Some people can pass a polygraph while lying, and innocent people may fail a lie detector test due to fear or other factors.
How Are Polygraph Examinations Used?
Criminal Investigations
The use of polygraph exams in police investigations is pretty common. Defense attorneys may advise clients to undergo polygraph testing to convince prosecutors to drop weak charges. However, no defendant or witness can be forced to take a polygraph test.
Security Clearances
Federal government agencies such as the Department of Defense, Department of Justice, National Security Agency, the CIA, and state and local police departments often use lie detector tests as part of the process to screen potential applicants for security clearances.
Employment Screening
Some companies may ask workers to a polygraph test. Truth is in demand, especially in the corporate world. To deal with cases of fake CVs, businesses are turning to their new best friend — the polygraph machine. Many firms are now approaching private forensic laboratories to conduct polygraph (lie-detection) tests on employees.
Company Investigations
Companies may use polygraph tests to investigate internal theft, fraud, or other misconduct. This can help in identifying employees involved in unethical activities.
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