What Is a Polygraph Test? - History, Reliability & Accuracy

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  • 0:04 Detecting Deception
  • 0:31 Polygraph Test History
  • 3:00 Reliability & Accuracy
  • 4:32 Polygraph Testing…
  • 5:35 Lesson Summary
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Lesson Transcript
Instructor: Amy C. Evans

Amy has a BA/MA Criminal Justice. Worked with youth for over 20 years in academic settings. Avid reader, history and mystery lover.

The polygraph test is the subject of this lesson. We'll discuss the history of the polygraph machine, its reliability, and how accurate the test is in the detection of deception.

Detecting Deception

How do you detect deception? This is a question that has plagued people for centuries. More modern techniques involve the study of body language, non-verbal communication, and how words are used and their tone to try and discover whether a person is lying or truthful. One of the most controversial methods, however, is that of the polygraph test. Let us dig in and learn more about this machine that attempts to get at the truth.

Polygraph Test: History

Let us first define what a polygraph test is. A polygraph test is a test that measures the body's physical responses to questions that are aimed at obtaining truthful information. One of the earliest attempts at measuring truthfulness using physical responses was Lombroso's Glove. Lombroso's Glove was invented by Italian criminologist Cesare Lombroso, and it was a technique used in the late 1800s in which the person being tested put their hand in a rubber glove that was then immersed in water. The person's flow of blood was then measured while their hand was in the water; lowered blood pressure was seen as a sign of deception.

American psychologist William M. Marston, who, interestingly enough, invented the iconic superhero Wonder Woman, is also sometimes referred to as the father of the lie detector. He was intrigued with the idea of truth finding and the connection between physical responses and emotions, and as a result, began working in 1915 on a machine to measure systolic blood pressure to explore this connection and determine whether a person was being deceitful or truthful. He tried to convince the U.S. military during World War I to investigate espionage, but the military did not trust the accuracy of the invention and did not adopt it for their investigations. Marston later refined his invention to add respiration as a measurable variable, and it was used occasionally on someone when they testified in court.

In the 1921, John Larson, a Berkeley University of California campus police officer who was working on his PhD in physiology, invented what we call today the polygraph, along with Leonard Keeler, also a police officer. It was called at the time the cardio-pneumo psychograph. The polygraph they invented measured physical responses to questions in the areas of respiration and blood pressure. Larson used Marston's work as a foundation to build upon.

Leonard Keeler worked with Larson on the invention and later made improvements to it that included cutting the amount of time to set up the device and the use of ink for recording the results. His improved version received a patent in 1931 and was the first ever patent awarded for a polygraph. In 1939, Keeler added a third area to be measured: changes in skin reactivity, such as sweating. Keeler later established a school for polygraph testing called the Keeler Polygraph Institute.

Reliability & Accuracy

While polygraph tests may provide some insight or guidance, they are not consistently reliable or accurate. Polygraphs can get things wrong, and people can manipulate these tests by manipulating their emotion responses to the questions, thus controlling the vital signs being measured.

A polygraph test may be able to detect, in some general way, that someone is being deceptive but not be able to accurately link the deception with any specificity to a criminal act.

Variables that affect the accuracy of tests include:

  • Drug use, prescribed medications for conditions such as anxiety and hypertension
  • Illegal drugs and alcohol
  • Inexperienced or unreliable examiners
  • The environment in which the test is applied (quiet or noisy, hot or cold, comfortable seating or uncomfortable seat, etc.)
  • The mental health of the person being tested
  • The intelligence of the person being tested
  • The presence of a personality disorder, like psychopathy, in the individual questioned
  • Gender and ethnicity can also play a role in the validity of a polygraph test

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