AskDefine | Define polygraph

Dictionary Definition

polygraph n : a medical instrument that records several physiological processes simultaneously (e.g., pulse rate and blood pressure and respiration and perspiration)

User Contributed Dictionary



  1. a device which measures and records several physiological variables such as blood pressure, heart rate, respiration and skin conductivity while a series of questions is being asked, in an attempt to detect lies.


Extensive Definition

A polygraph (commonly referred to as a lie detector) is an instrument that measures and records several physiological responses such as blood pressure, pulse, respiration and skin conductivity while the subject is asked and answers a series of questions, on the basis that false answers will produce distinctive measurements. The polygraph measures physiological changes caused by the sympathetic nervous system during questioning. Within the U.S. federal government , a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination. Several other technologies are also used in the field of lie detection, but the polygraph is the most famous.


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 was dry.
Early devices for lie detection include an 1885 invention of Cesar Lombroso used to measure changes in blood pressure for police cases, a 1914 device by Vittorio Benussi used to measure breathing, and an abandoned project by American William Marston which used blood pressure and galvanic skin response to examine German prisoners of war.
A device recording both blood-pressure and galvanic skin response was invented in 1920 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. Further work on this device was done by Leonarde Keeler. The first time the term "polygraph" was used was in 1906 by James MacKenzie in his invention the "ink polygraph," which was used for medical reasons.
Makenzie 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. According to their son, Marston's wife, Elizabeth Holloway Marston, was also involved in the development of the systolic blood-pressure test: "According to Marston’s son, it was his mother Elizabeth, Marston’s wife, who suggested to him that 'When she got mad or excited, her blood pressure seemed to climb' (Lamb, 2001). Although Elizabeth is not listed as Marston’s collaborator in his early work, Lamb, Matte (1996), and others refer directly and indirectly to Elizabeth’s work on her husband’s deception research. She also appears in a picture taken in his polygraph laboratory in the 1920s (reproduced in Marston, 1938)." The comic book character, Wonder Woman by William Marston (and influenced by Elizabeth Marston ) carries a magic lasso which was modelled upon the systolic blood-pressure test. In 1938 he appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.

Testing procedure

globalise section 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 CQ. 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 ("Is your name Rob T?"), 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 RQ, 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 (CQ) are larger than those during the relevant questions (RQ). If this is not the case, the tester attempts to elicit admissions during a post-test interview, for example, "Your situation will only get worse if we don't clear this up".
Criticisms have been given regarding the validity of the administration of the Control Questions test (CQT). The CQT may be vulnerable to be conducted in an interrogation-like fashion. This kind of interrogation style would elicit a nervous response from innocent and guilty suspects alike. There are several other ways of administrating the questions.
An alternative is the Guilty Knowledge test (GKT), or the Concealed Information Test (CIT). The administration of this test if given to prevent potential errors that may arise from the questioning style. The test is usually conducted by a tester with no knowledge of the crime or circumstances in question. The administrator tests the participant on their knowledge of the crime that would not be known to an innocent person. For example: “Was the crime committed with a .45 or a 9 mm?” The questions are in multiple choice and the participant is rated on how they react to the correct answer. If they react strongly to the guilty information, then proponents of the test believe that it is likely that they know facts relevant to the case. This administration is considered more valid by supporters of the test because it contains many safeguards to avoid the risk of the administrator influencing the results.


There is little scientific evidence to support the reliability of polygraphs. Despite claims of 90% - 95% reliability, critics charge that rather than a "test", the method amounts to an inherently unstandardizable interrogation technique whose accuracy cannot be established. A 1997 survey of 421 psychologists estimated the test's average accuracy at about 61%, a little better than chance. 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. In the 1998 Supreme Court case, United States v. Scheffer, the majority stated that “There is simply no consensus that polygraph evidence is reliable” and “Unlike other expert witnesses who testify about factual matters outside the jurors' knowledge, such as the analysis of fingerprints, ballistics, or DNA found at a crime scene, a polygraph expert can supply the jury only with another opinion...”. Also, in 2005 the 11th Circuit Court of Appeals stated that “polygraphy did not enjoy general acceptance from the scientific community”. In 2001 William G. Iacono, Distinguished McKnight University Professor of Psychology and Neuroscience and Director, Clinical Science and Psychopathology Research Training Program at the University of Minnesota, published a paper titled “Forensic “Lie Detection": Procedures Without Scientific Basis” in the peer reviewed Journal of Forensic Psychology Practice. He concluded that Although the CQT [Control Question Test] may be useful as an investigative aid and tool to induce confessions, it does not pass muster as a scientifically credible test. CQT theory is based on naive, implausible assumptions indicating (a) that it is biased against innocent individuals and (b) that it can be beaten simply by artificially augmenting responses to control questions. Although it is not possible to adequately assess the error rate of the CQT, both of these conclusions are supported by published research findings in the best social science journals (Honts et al., 1994; Horvath, 1977; Kleinmuntz & Szucko, 1984; Patrick & Iacono, 1991). Although defense attorneys often attempt to have the results of friendly CQTs admitted as evidence in court, there is no evidence supporting their validity and ample reason to doubt it. Members of scientific organizations who have the requisite background to evaluate the CQT are overwhelmingly skeptical of the claims made by polygraph proponents.
Polygraph tests have also been criticized for failing to trap known spies such as double-agent Aldrich Ames, who passed two polygraph tests while spying for the Soviet Union. Other spies who passed the polygraph include Karl Koecher, Ana Belen Montes, and Leandro Aragoncillo. Pseudoscience debunker Bob Park said, "The polygraph, in fact, has ruined careers, but never uncovered a single spy." Polygraph examination and background checks also failed to detect Nada Nadim Prouty, who was not a spy but was convicted for improperly obtaining US citizenship and using it to obtain a restricted position at the FBI.
Some studies have shown the presence of a phenomenon called "confusional states". In these phenomena the interviewee, unconsciously, don’t tell the truth about a certain situation. This happens when the interviewee is subjected to a particular stress due to the question. In fact, when the questions insinuate the interviewee’s non morality, the candidate, sometimes (very rarely), will respond false, even if unconsciously and although in strong contrast with his beliefs.
Prolonged polygraph examinations are sometimes used as a tool by which confessions are extracted from a defendant, as in the case of Richard Miller, who was persuaded to confess largely by polygraph results combined with appeals from a religious leader.


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. 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."

2003 National Academy of Sciences report

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. 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.” 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 if the test were sensitive enough to detect 80% of spies (a level of accuracy which it did not assume), in a hypothetical polygraph screening of 10,000 employees including 10 spies, 8 spies and 1,598 non-spies would fail the test. Thus, roughly 99.6 percent of positives (those failing the test) would be false positives. The NAS concluded that the polygraph “...may have some utility” but that there is "little basis for the expectation that a polygraph test could have extremely high accuracy."
The NAS conclusions paralleled those of the earlier United States Congress Office of Technology Assessment report "Scientific Validity of Polygraph Testing: A Research Review and Evaluation”.

Admissibility of polygraphs in court

United States

In 2007, polygraph testimony was admitted by stipulation in 19 states, and was subject to the discretion of the trial judge in federal court. The use of polygraph in court testimony remains controversial, although it is used extensively in post-conviction supervision, particularly of sex offenders. In Daubert v. Merrell Dow Pharmaceuticals (1993), the old Frye standard was lifted and all forensic evidence, including polygraph, had to meet the new Daubert standard in which "underlying reasoning or methodology is scientifically valid and properly can be applied to the facts at issue." 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), the U.S. 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. In the States of Massachusetts, Maryland, New Jersey, Delaware and Iowa it is illegal for any employer to order a polygraph either as conditions to gain employment, or if an employee has been suspected of wrongdoing. The Employee Polygraph Protection Act of 1988 (EPPA) generally prevents employers from using lie detector tests, either for pre-employment screening or during the course of employment, with certain exemptions.
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 2007, in Ohio v. Sharma, an Ohio trial court overruled the objections of a prosecutor and allowed a polygraph examiner to testify regarding a specific issue criminal examination. The court took the position that the prosecutors regularly used polygraph examiner to conduct criminal tests against defendants, but only objected to the examiner's testimony when the results contradicted what they hoped to achieve. Dr. Louis Rovner,, a polygraph expert from California, tested the defendant and testified as an expert witness both at a pretrial admissibility hearing and at trial. The defendant, who had been charged with sexual battery, was acquitted.


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 one's testimony by submitting themselves to a polygraph session.


In Canada, the polygraph is regularly used as a forensic tool in the investigation of criminal acts and sometimes employed in the screening of employees for government organizations. In the 1987 decision of R. v. Béland, the Supreme Court of Canada rejected the use of polygraph results as evidence in court. This decision did not however affect the use of the polygraph in criminal investigations. The polygraph continues to be used as an investigative tool.


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.


The High Court of Israel, in Civil Appeal 551/89 (Menora Insurance Vs. Jacob Sdovnik), ruled that as the polygraph has not been recognized as a reliable device, polygraph results are inadmissible as evidence in a civil trial. In other decisions, polygraph results were ruled inadmissible in criminal trials. However, some insurance companies attempt to include a clause in insurance contracts, in which the beneficiary agrees that polygraph results be admissible as evidence. In such cases, where the beneficiary has willingly agreed to such a clause, signed the contract, and took the test, the courts will honor the contract, and take the polygraph results into consideration. Interestingly, it is common practice for lawyers to advise people who signed such contracts to refuse to take the test. Depending on whether or not the beneficiary signed an agreements clause, and whether the test was already taken or not, such a refusal usually has no ill effects; At worst, the court will simply order the person to take the test as agreed. At best, the court will cancel the clause and release the person from taking the test, or rule the evidence inadmissible.

Use with espionage and security clearances

In the American military and intelligence communities, polygraphs have been administered both as terms of qualifying for a security clearance and as part of a periodic reinvestigation to retain a clearance. There is no uniform standard for whether the polygraph is needed, as some methods of adjudication do not demand a successful polygraph test to earn a clearance. Other agencies, particularly certain military units, actually prohibit polygraph testing on their members.
It is difficult to precisely determine the effectiveness of polygraph results for the detection or deterrence of spying. Failure of a polygraph test could cause revocation of a security clearance, but it is inadmissible evidence in most federal courts and military courts martial. The polygraph is more often used as a deterrent to espionage rather than detection. One exception to this was the case of Harold James Nicholson, a CIA employee later convicted of spying for Russia. In 1995, Nicholson had undergone his periodic five year reinvestigation where he showed a strong probability of deception on questions regarding relationships with a foreign intelligence unit. This polygraph test later launched an investigation which resulted in his eventual arrest and conviction. In most cases, however, polygraphs are more of a tool to "scare straight" those who would consider espionage. Jonathan Pollard was advised by his Israeli handlers that he was to resign his job from American intelligence if he was ever told he was subject to a polygraph test. Likewise, John Anthony Walker was advised to by his handlers not to engage in espionage until he had been promoted to the highest position, for which a polygraph test was not required, to refuse promotion to higher positions for which polygraph tests were required, and to retire when promotion was mandated. As part of his plea bargain agreement for his case of espionage against the Soviet Union, Robert Hanssen would be made to undergo a polygraph at any time as part of damage assessment. In Hanssen's 25-year career with the FBI, not once was he made to undergo a polygraph. He later said if he had been ordered; he may have thought twice about espionage.
Alternatively, the use of polygraph testing, where it causes desperation over dismissal for past dishonesty, may encourage spying. For example, Edward Lee Howard was dismissed from the CIA after polygraph screens targeted a series of minor crimes such as petty theft and drug abuse, and later sold his knowledge of CIA operations to the Soviet Union.
It is also worth noting that polygraph tests may not deter espionage. From 1945 to the present, at least six Americans had been committing espionage while they successfully passed polygraph tests. Two of the most notable cases of two men who created a false negative result with the polygraphs were Larry Wu-Tai Chin and Aldrich Ames.

Hand-held lie detector for U.S. military

A hand-held lie detector is being deployed by the U.S. Defense Department, according to a report in 2008 by investigative reporter Bill Dedman of The Preliminary Credibility Assessment Screening System, of PCASS, captures less physiological information than a polygraph, and uses an algorithm, not the judgement of a polygraph examiner, to render a decision whether it believes the person is being deceptive or not. The device will be used first in Afghanistan by U.S. Army troops. It can be used only on non-U.S. persons.

Use with sex offenders

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 committed a further offense 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 will soon allow compulsory polygraph tests for convicted sex offenders released on license.

Polygraph in popular culture

Lie detection has a long history in mythology and fairy tales; the polygraph has allowed modern fiction to use a device more easily seen as scientific and plausible. Notable instances of polygraph usage include uses in crime and espionage themed television shows and some daytime television talk shows, cartoons and films. The most notable polygraph TV show is Lie Detector, which first aired in the 1950s created and hosted by Ralph Andrews. Then in the 1960s Ralph produced a series of specials hosted by Melvin Belli, then in the 1970s hosted by Jack Anderson. In 1998 TV producer Mark Phillips with his Mark Phillips Philms & Telephision put Lie Detector back on the air on the FOX Network -- on that program Dr. Ed Gelb with host Marcia Clark cleared Mark Fuhrman from the allegation that he "planted the bloody glove." Later Phillips produced Lie Detector as a series for PAX/ION -- some of the guests included Paula Jones, Reverend Paul Crouch accuser Lonny Ford, Ben Rowling, Jeff Gannon and Swift Boat Vet Steve Garner.
FOX has taken this one step further with their game show The Moment of Truth which pits people's honesty against their own sense of modesty, propriety, etc. Contestants are given a polygraph test administered by a polygraph expert in a pre-screening session answering over 50 questions. Later they must sit in front of a studio audience including their friends & family for the televised portion of the show. There they need only answer 21 answers truthfully "as determined by the polygraph" to win $500,000. The questions get more personal and/or more revealing as they advance.
Daytime talk shows, such as Maury Povich, frequently uses lie detectors in order to tell if someone is cheating on their significant other.
In the movie Ocean's 13, one of the characters beats a polygraph test by stepping on a tack when answering truthfully, which supposedly raises the polygraph's readings for the truthful answers so they equal to the deceptive ones.
In episode 109 see video clip of the popular science show Mythbusters, they attempted to fool the polygraph by using pain to try and increase the readings when answering truthfully (so the machine will supposedly interpret the truthful and non-truthful answers as the same.) They also attempted to fool the polygraph by thinking happy thoughts when lying and thinking stressful thoughts when telling the truth to try and confuse the machine. However, neither technique was successful and the examiner Michael Martin correctly identified each guilty and innocent subject. The show also noted the widely held opinion that, when done properly, polygraphs are correct 80-99% of the time.


Further reading

  • Alder, Ken (2007) The Lie Detectors: The History of an American Obsession. (New York: The Free Press, 2007)
  • Blinkhorn, S. (1988) "Lie Detection as a psychometric procedure" In "The Polygraph Test" (Gale, A. ed. 1988) 29-39.
  • Lykken, D.T. (1998) A Tremor in the Blood: Uses and Abuses of the Lie Detector. 2nd edition. (New York: Plenum Trade, 1998).
  • Roese, N. J., & Jamieson, D.W. (1993). Twenty years of bogus pipeline research: A critical review and meta-analysis. Psychological Bulletin, 114, 363-375.
  • Sullivan, John F. (2008) Gatekeeper: Memoirs of a CIA Polygraph Examiner. Potomac Books.

External links

polygraph in Arabic: جهاز كشف الكذب
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