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The History and Basic Facts of Polygraph

The history of civilization is filled with attempts to detect lies and to verify the truth. During the 18th century some methods of detection included the Ordeal of Boiling Water. In this test the subject would stick his hand in a pot of boiling water and if his hand did not suffer a burn, he was believed to be telling the truth. Not too many people passed that test! There was another very similar test called the Ordeal of the Red-Hot Stones. Like the first ordeal this was a lie test to see if God was on your side and without His divine help you would have never passed this test. You would walk across red-hot stones and if your feet did not burn, you were believed to be telling the truth. No one really passed these tests because they rarely gave them to innocent people. As time marched on and man made improvements in his lie detection, he based the lie test on pure chance. For instance, truth or lack of truth might be determined by a throw of a knife, or the pattern of a handful of tossed stones. As most of you might have guessed these methods were neither reliable nor scientific but at least they were a little more humane.

An Italian criminologist, Cesare Lombroso, developed the earliest scientific approach. In 1895 he conducted experiments in the detection of deception by attempting to record changes in the subject's blood pressure with a device called "Lombroso's Glove." Unfortunately, his main interest was in criminal identification through physical characteristics and he never had the time to continue with his experiments in lie detection. Later another Italian named Mosso conducted further investigations of blood-volume changes during deception tests by using a crude device known as "Mosso's Cradle".

Around the beginning of the First World War another Italian, Vittorio Benumbs, conducted experiments in lie detection with a device that measured and recorded the rate and depth of the subject's respiration. These experiments convinced him that changes take place in the respiratory pattern when a person attempted to lie or deceive. These same beliefs hold true even today with modern polygraph examiners.

In 1932 a Russian, A. R. Luria, made an important contribution. He wrote that a criminal trying to conceal his guiltiness grows more and more tense and thus finds it harder and harder to remain passive under questioning.

Also during World War I the United States Government commissioned a psychologist, Dr. William M. Marston, to devise a method for the questioning of prisoners of war. Using a sphygmomanometer, a device physicians use to take a patient's blood pressure, he conducted experiments by taking intermittent readings of the blood pressure during questioning.

In 1921 the Berkeley, California Police Department encouraged Dr. John A. Larson, a psychiatrist, to develop what became the forerunner of the modern-day polygraph. The instrument made the first permanent record of blood pressure, pulse, and respiration. This original polygraph was used for many years by the Berkeley Police Department and enabled Dr. Larson to identify correctly many hundreds of criminals, as well as thousands of innocent persons who would have been suspected of crimes.

Leonard Keeler, a psychologist, became interested in the technique and developed his own instrument which had the added feature of measuring changes in the skin's resistance to electricity, commonly known as "galvanic skin response."

Keeler is generally recognized as the father of the modern-day polygraph. He combined three important components that are still used today even though through modern electronics these components are now greatly enhanced. These three things are the pneumograph, cardiograph and the galvanic skin response. Some of the more modern machines have added other electronic devices but Keeler's three main components are contained in the present-day polygraph instrument.

The first major case dealing with the use of polygraph in criminal cases was tried in 1923. This case set a precedent in polygraph. In Frye vs. United States the court ruled that polygraph was inadmissible based on the general acceptance rule of scientific reliability. The Frye case involved a man accused of murder. Even though Frye claimed that he was innocent, a jury found him guilty. Before his trial Frye was given a polygraph. A researcher by the name of Marston gave the opinion that Frye was telling the truth. Marston used blood pressure changes as indicators for truthful or deceptive responses. After serving about three years of his prison sentence another man confessed to the murder and Frye was released.

July 1981 brought a legal change involving polygraph. Prior to July 1981, stipulation between prosecution and defense was a vehicle for the admittance of Polygraph. However, the July 1981 ruling disallowed that stipulation. At present, only a statement (confession) is admissible at trial level. Law enforcement agencies today utilize polygraph as an investigative tool.


Today, every major law enforcement agency, every state police organization, and every large and middle size city police department has a polygraph operation. While many small cities and rural sheriff's offices also have examiners, others depend on state assistance. Public defenders' offices are often staffed with examiners, as are states attorney's offices and other agencies in the criminal justice system.

In the Federal Government, the Federal Bureau of Investigation, the Drug Enforcement Agency, and the United States Secret Service, Customs, and similar agencies regularly use the polygraph. The divisions involved in criminal investigations and intelligence of the Army, Navy, Air Force and Marine Corps use the polygraph, as do the major intelligence agencies, including the Central Intelligence Agency. The polygraph is not confined to the United States. It is regularly used by law enforcement agencies in Canada, Japan and Israel, and to a lesser extent by law enforcement agencies in more than twenty other nations.

In addition to its role in law enforcement and intelligence, the polygraph plays a significant role in the security of industry. Over 26% of the major companies in the United States now use polygraph. However they must not comply with the American Polygraph Protection Act and now restrictions do apply. The pre-screening of applicants and the use of polygraph for discovering the source of specific thefts are common, particularly among those industries that are particularly susceptible to thefts by employees. Drug manufacturers, distributors, and handlers annually suffer huge losses to organized crime. The trucking and warehousing industries also pass on to the consumers the excessive losses from theft and pilfering. Polygraph screening is also employed to protect the public from unfit airline pilots and others whose skill and well-being involves public safety. Examiners who are employees of the company or agency or by companies and individuals who specialize in polygraph service may conduct polygraph examinations in industry and public service. Polygraph is now being use in the treatment of sexual offenders to help keep us safe from sexual criminals.


Theory of Polygraph

  1. Psychological Theory of a lie: Emotional changes occur in a person causing physiological changes that can be recognized and diagnosed.
  2. Psychological Set . . . A person's fears, anxieties and apprehensions are focused (directed) to the areas that hold (Poses) the greatest threat to his well being or self.
  3. Psychology of Test Questions The test is structured so as to pose a threat to the security of both the innocent and guilty subject and force him/her to focus (direct) his/her attention to that specific area of the test.

**Fear is the greatest psychological factor - Fear of being detected of an untruth.

The administration of the polygraph examination requires the monitoring of the physiological changes that occur during the process of the examination. Three specific physical factors are measured:

  1. Respiration System
    Components called pneumographs, rubber convoluted tubes, record respiration. They are attached around the examinee's waist and chest. As the person breathes, these tubes stretch and contract, causing pressure changes within the tubes.
  2. Galvanic Skin Response (GSR)
    GSR is electrical in nature. Metal contacts are attached to two of the examinee's fingers. They record apparent changes in skin resistance to electricity. Emotional sweat glands, faradic skin, become active as a result of arousal/stress (skin acts as resistance factor).
  3. Cardiovascular System
    The cardio activity is monitored by the use of a blood pressure cuff similar to the type used in the medical profession. It is generally fastened to the upper arm to monitor changes in relative blood pressure and pulse rate.

There are three phases to a polygraph examination: Pretest, Chart Collection, and Post-test.


The pre-test examination is probably the single most important part of any polygraph test. The person to be tested in most cases is apprehensive or fearful. He may be upset at being suspected of wrong doing, nervous, angry and suspicious. Thoughts of inaccuracy of the instrument or whether or not the examiner will be fair are not the exception.

During the pre-test, the examiner attempts to build a rapport with the examinee. It is an information gathering session. The information is of a personal and factual nature and reflects the examinee's entire past and present. It is essential for the examiner to feel like he "knows" the person he is to examine and for the examinee to feel that he is to be tested fairly. Additionally, no examination will be given unless it is voluntary. Forms relating to the voluntary, waiver (civil litigation) and Miranda are signed before the per-test begins.

It is necessary for the individual to understand the concept of polygraph and what he/she is about to experience. The more thorough the examiner explains the theory of polygraph and convinces the individual of the procedure and effectiveness, the better the test. He/she must be convinced that "the polygraph works". If he is innocent, he will be found innocent if he is guilty, he will be found guilty.

It is necessary to explain to the examinee how physiological responses give an indication of truthfulness or deception. To the examinee: ''let's imagine that you are in a hallway having idle conversation and someone steps around the corner and fires a gun. You are immediately threatened. Certain things happen to you physically. Your heart may feel like it's in your throat, or it's going to pound out of your chest, you can hardly breathe, you feel warm all over. What is happening to you is physiology that you can't control. All these things occur in an involuntary manner. You are in fear for your well-being and are prepared to either fight or take flight. That same situation happens in a polygraph setting. The threat is not the gun but the threat of being detected of intentionally lying. There is a gun inside of you, cocked and loaded, that goes off and simultaneously causes the same physiological changes to occur that occurred in the hall. You can't prevent them from happening now anymore than you could before. The polygraph will record those changes. The examiner will know when those changes occur."

It is also necessary for the examiner to know the case facts. Prior to actual introduction of the person to be examined, he has gone over the case in great detail with the investigator the examiner lets the individual tell his side of the story or reason for taking the polygraph. Points of clarification are made so that there is a mutual understanding of what the examinee is trying to convey to the examiner. The examiner must always remember that this is an interview process and NOT AN INTERROGATION.

At this point, the examiner chooses which type of test is best suited for that individual and circumstances of the Case.


There are only two types of tests, Comparison and Non comparison tests and there are several variations to both types.


  1. Irrelevant
  2. Relevant
  3. Control
  4. Symptomatic

Test questions are formulated by the examiner and completely reviewed with the examinee. The examinee must know and completely understand each question. He/she is also advised that these questions and only these questions will be asked during the course of the examination.

Basically, there are three types of questions. There are those questions (irrelevant) designed to establish a normal tracing average of responses during the test. They have little or no intensity to them. There are questions relevant to the issue or incident for which the polygraph test is being administered. There are control questions. Control questions are designed to be somewhat vague or ambiguous and create doubt in the examinee's mind as to the truthfulness of his answers.

Instructions are given to the examinee as to how the actual examination will proceed.

Chart Collection

Chart collection is the actual polygraph examination. The formulated and reviewed questions are asked a minimum of two (2) complete times. Normally, three (3) complete charts are obtained. A "Stimulation test" may also be given to monitor subject's response capabilities.


During Post-test, the examiner makes an analysis, most the time after the examinee leaves or if time permits while the examinee waits, of physiological responses and determines whether the responses indicate truthfulness or deception. Each question and response activity to that question is evaluated. A comparison is made to other questions and that response activity, i.e., Relevant vs. Irrelevant, Relevant vs. Control. A computer algorithm and a numerical scoring system are often applied for evaluation purposes. The examiner then renders an opinion. That opinion either is truthful, deceptive or inconclusive. An inconclusive opinion is given when the examiner cannot determine from the responses whether the person is truthful or deceptive. Responses are either distorted, non-responsive, or over-responsive to all quest ions - in these cases a reexamination is normally suggested.

Post-test also includes an interrogation period should the examinee indicate deception (If requested by the client). Should a statement (confession) be obtained, that statement could be used against the examinee in a criminal or administrative proceeding.

The results of the examination are then given in oral and report form to the requester of the polygraph examination.


Abrams, S. and Ansley, N. The Polygraph Profession,

1980.Potvin, Robert. Unpublished paper on Introduction to Polygraph 1983.

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