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Lie detector test redirects here.
Patent 4333084

Polygraph results are sometimes recorded on a chart recorder

A polygraph (commonly yet incorrectly referred to as a lie detector) is a device that measures and records several physiological variables such as blood pressure,respiration and skin conductivity while the subject is asked a series of questions. The measurements are posited to be indicators of anxiety that accompanies the telling of lies. Thus, measured anxiety is equated with telling untruths. However, if the subject exhibits anxiety for other reasons, or can control his anxiety level voluntarily, a measured response can result in unreliable conclusions. A polygraph test is also questionably used as a psychophysiological detection of deception (PDD) examination.


The idea that lying produces physical side-effects has long been claimed. In West Africa persons suspected of a crime were made to pass a bird's egg to one another. If a person broke the egg, then he or she was considered guilty, based on the idea that their nervousness was to blame. In Ancient China the suspect held a handful of rice in his or her mouth during a prosecutor's speech. Since salivation was believed to cease at times of emotional anxiety, the person was considered guilty if by the end of that speech the rice remained.

The origins of the modern polygraph date to 1913, when William Moulton Marston, a psychology student at Harvard University, first used the systolic blood-pressure test as a method of lie detection. He wrote a second paper on the concept in 1915, when finishing his undergraduate studies. He entered Harvard Law School and graduated in 1918, re-publishing his earlier work in 1917. A more complex device recording both blood-pressure and galvanic skin response was invented by Dr. John A. Larson of the University of California and first applied in law enforcement work by the Berkeley Police Department under its nationally-renowned police chief August Vollmer. Larson's device was the first that could be referred to as a polygraph, as Marston's earlier device recorded only one graph.

Marston nevertheless remained the device's primary advocate, endlessly lobbying for its use in the courts. In 1938 he published a book, The Lie Detector, where he documented the theory and use of the device. Nevertheless he was not above a little faked publicity, and in 1938 appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.[1] [2] [3]

Testing ProcedureEdit

Today, polygraph examiners use two types of instrumentation, analog and computerized. In the United States, most examiners now use computerized instrumentation.

A typical polygraph test starts with a pre-test interview to gain some preliminary information which will later be used for "Control Questions", or C. Then the tester will explain how the polygraph is supposed to work, emphasizing that it can detect lies and that it is important to answer truthfully. Then a "stim test" is often conducted: the subject is asked to deliberately lie and then the tester reports that he was able to detect this lie. Then the actual test starts. Some of the questions asked are "Irrelevant " or IR ("Are you 35 years old?"), others are "probable-lie" Control Questions that most people will lie about ("Have you ever stolen money?") and the remainder are the "Relevant Questions ", or R, that the tester is really interested in. The different types of questions alternate. The test is passed if the physiological responses during the probable-lie control questions (C) are larger than those during the relevant questions (R). If this is not the case, the tester attempts to elicit admissions during a post-test interview ("Your situation will only get worse if we don't clear this up").[4] [5]

While some people believe that polygraph tests are reliable, there is little scientific evidence to buttress this claim. For example, while some claim the test to be accurate in 70% - 90% of the cases, critics charge that rather than a "test", the method amounts to an inherently unstandardizable interrogation technique whose accuracy cannot be established. Critics also argue that even given high estimates of the polygraph's accuracy a significant number of subjects (e.g. 10% given a 90% accuracy) will appear to be lying, and would unfairly suffer the consequences of "failing" the polygraph. Polygraph tests have also been criticized for failing to trap known spies such as Aldrich Ames, who passed two polygraph tests while spying for the Soviet Union.[6] Other spies who passed the polygraph include Karl Koecher,[7] Ana Belen Montes,[8] and Leandro Aragoncillo.[9]

Several countermeasures designed to pass polygraph tests have been described, the most important of which is never to make any damaging admissions. Additionally, several techniques can be used to increase the physiological response during control questions.[10] Asked how he passed the polygraph test, Ames explained that he sought advice from his Soviet handler and received the simple instruction to: "Get a good night's sleep, and rest, and go into the test rested and relaxed. Be nice to the polygraph examiner, develop a rapport, and be cooperative and try to maintain your calm."[11]

2003 National Academy of Sciences ReportEdit

The accuracy of the polygraph has been contested almost since the introduction of the device. In 2003, the National Academy of Sciences (NAS) issued a report entitled “The Polygraph and Lie Detection”. The NAS found that the majority of polygraph research was of low quality. It is interesting to note that, so far, no scientific study has been published that offers convincing evidence of the validity of the polygraph test. After culling through the numerous studies of the accuracy of polygraph detection the NAS identified 57 that had “sufficient scientific rigor”. These studies concluded that a polygraph test regarding a specific incident can discern the truth at “a level greater than chance, yet short of perfection”. The report also concluded that this level of accuracy was probably overstated and the levels of accuracy shown in these studies "are almost certainly higher than actual polygraph accuracy of specific-incident testing in the field.” [6]

When polygraphs are used as a screening tool (in national security matters and for law enforcement agencies for example) the level of accuracy drops to such a level that “Its accuracy in distinguishing actual or potential security violators from innocent test takers is insufficient to justify reliance on its use in employee security screening in federal agencies.” In fact, the NAS extrapolated that 10,000 polygraph tests searching for spies would incorrectly classify 99.5% of “deceptive” results (those telling the truth yet incorrectly deemed to be deceitful), and incorrectly classify 20% of deceitful subjects. The NAS concluded that the polygraph “…may have some utility” [7] but that there is "little basis for the expectation that a polygraph test could have extremely high accuracy."[8]

The NAS conclusions were the same as those in the earlier United States Congress Office of Technology Assessment report "Scientific Validity of Polygraph Testing: A Research Review and Evaluation”.[9]

Admissibility of polygraphs in CourtEdit

United StatesEdit

While polygraph tests are commonly used in police investigations in the US, no defendant or witness can be forced to undergo the test. In United States v. Scheffer (1998) [10], the US Supreme Court left it up to individual jurisdictions whether polygraph results could be admitted as evidence in court cases. Nevertheless, it is used extensively by prosecutors, defense attorneys, and law enforcement agencies who believe in its utility.

In the United States, the State of New Mexico admits polygraph testing in front of juries under certain circumstances. In many other states, polygraph examiners are permitted to testify in front of judges in various types of hearings (Motion to Revoke Probation, Motion to Adjudicate Guilt).


In most European jurisdictions, polygraphs are not considered reliable evidence and are not generally used by police forces. However, in any lawsuit, an involved party can order a psychologist to write an opinion based on polygraph results to substantiate the credibility of its claims. The party must bear the expense themselves, and the court weighs the opinion like any other opinion the party has ordered. Courts themselves do not order or pay for polygraph tests. An example of this practice would be a rape trial in which the defendant tries to fortify their testimony by submitting themselves to a polygraph session.


In Canada, the use of a polygraph is sometimes employed in screening employees for government organizations. However, in the 1987 decision of R. v. Béland, the Supreme Court of Canada rejected the use of polygraph results as evidence in court.


The High Court of Australia has not yet considered the admissibility of polygraph evidence. However, the New South Wales District Court rejected the use of the device in a criminal trial. In Raymond George Murray 1982 7A Crim R48 Sinclair DCJ refused to admit polygraph evidence tending to support the defence. His Honour rejected the evidence because:

  1. The veracity of the accused and the weight to be given to his evidence, and other witnesses called in the trial, was a matter for the jury.
  2. The polygraph "expert" sought to express an opinion as to ultimate facts in issue, which is peculiarly the province of the jury.
  3. The test purported to be expert evidence by the witness who was not qualified as an expert, he was merely an operator and assessor of a polygraph. The scientific premise upon which his assessment was based had not been proved in any Court in Australia.
  4. Devoid of any proved or accepted scientific basis, the evidence of the operator is hearsay which is inadmissible.

The Court cited, with approval, the Canadian case of Phillion v R 1978 1SCR 18.

Use with sex offendersEdit

Sexual offenders are now routinely polygraphed in many states of the United States and it is often a mandatory condition of probation or parole. In Texas, a state appellate court has upheld the testing of sex offenders under community supervision and has also upheld written statements given by sex offenders if they have re-offended with new victims. These statements are then used when a motion is filed to revoke probation and the probationer may then be sentenced to prison for having violated his or her probation.

A significant number of Federal appeals courts have upheld polygraph testing for Federal probationers as well. The most recent decision was by the Second Circuit Court of Appeals regarding a New York sex offender.

The UK is considering compulsory lie detector tests for sex offenders.[11]


  1. William Marston's Secret Identity. Reason magazine.
  2. Now! Lie Detector Charts Emotional Effects of Shaving - 1938 Gillette Advertisement [1]
  3. FBI File of William Moulton Marston (including report on Gillette advertising campaign) [2]
  4. For details on the intricacies of various polygraph techniques, see the Federal Psychophysiological Detection of Deception Examiner Handook, the U.S. Government's official guide to the administration of polygraph examinations. [3]
  5. For interrogation techniques associated with polygraph testing, see the Department of Defense Polygraph Institute's Interview & Interrogation Handbook. [4]
  6. Ames provides personal insight into the U.S. Government's reliance on polygraphs in a 2000 letter to Steven Aftergood of the Federation of American Scientists. [5]
  7. Kessler, Ron. "Moscow's Mole in the CIA: How a Swinging Czech Superspy Stole America's Most Sensitive Secrets," Washington Post, April 17, 1988, C1.
  8. Bachelet, Pablo Book outlines how spy exposed U.S. intelligence secrets to Cuba. McClatchey Washington Bureau. "She first came under U.S. suspicion in 1994, when Cuba detected a highly secret electronic surveillance system. Montes took a polygraph test and passed it."
  9. Ross, Brian and Richard Esposito. Investigation Continues: Security Breach at the White House. ABC News. "Officials say Aragoncillo passed several lie detector tests that are routinely given to individuals with top secret clearances."
  10. Lykken, David T. A Tremor in the Blood: Uses and Abuses of the Lie Detector, 2nd ed., New York: Plenum Trade, 1998, pp. 273-279.
  11. Weiner, Tim, David Johnston, and Neil A. Lewis, Betrayal: The Story of Aldrich Ames, an American Spy, 1995.


Further ReadingEdit

  • Blinkhorn, S. (1988) "Lie Detection as a psychometric procedure" In "The Polygraph Test" (Gale, A. ed. 1988) 29-39.

See alsoEdit

External linksEdit

et:Valedetektor es:Polígrafo fr:Détecteur de mensonge he:פוליגרף lt:Poligrafas nl:Leugendetectorpt:Polígrafo ru:Полиграф sr:Полиграф sv:Lögndetektoruk:Поліграф

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