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Polygraph Testing


A polygraph (popularly referred to as a lie detector) is an instrument that measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions, in the belief that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers.

Polygraphy is widely rejected as being pseudoscience by the scientific community. Nonetheless, polygraphs are in some countries used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. US federal government agencies such as the FBI and the CIA and many police departments such as the LAPD use polygraph examinations to interrogate suspects and screen new employees. Within the US federal government, a polygraph examination is also referred to 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 ostrich'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. Because 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 Cesare
Lombroso used to measure changes in blood pressure for police cases, a 1904 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 (POWs).

Marston 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 modeled upon the pneumograph (breathing monitor) test.

Marston was the self-proclaimed “father of the polygraph” despite his predecessor's contributions. Marston remained the device's primary advocate, lobbying for its use in the courts. In 1938 he published a book, The Lie Detector Test, wherein he documented the theory and use of the device. In 1938 he appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.

A device recording both blood pressure and galvanic skin response was invented in 1921 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.

Several devices similar to Keeler's polygraph version included the Berkeley Psychograph, a blood pressure-pulse-respiration recorder developed by C. D. Lee in 1936 and the Darrow Behavior Research Photopolygraph, which was developed and intended solely for behavior research experiments.

A device which recorded muscular activity accompanying changes in blood pressure was developed in 1945 by John E. Reid, who claimed that greater accuracy could be obtained by making these recordings simultaneously with standard blood pressure-pulse-respiration recordings. Testing procedure.

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 Chris?"), 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 Comparative Questions test (CQT). The CQT may be vulnerable to being 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 is 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.


Polygraphy has little credibility among scientists. Despite claims of 90-95% validity by polygraph advocates, and 95-100% by businesses providing polygraph services, critics maintain 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”. Charles Honts, a psychology professor at Boise State University, states that polygraph interrogations give a high rate of false positives on innocent people. 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.

Summarizing the consensus in psychological research, professor David W. Martin, PhD, from North Carolina State University, states that people have tried to use the polygraph for measuring human emotions, but there is simply no royal road to (measuring) human emotions. Therefore, since one cannot reliably measure human emotions (especially when one has an interest in hiding his/her emotions), the idea of valid detection of truth or falsehood through measuring respiratory rate, blood volume, pulse rate and galvanic skin response is a mere pretense. Since psychologists cannot ascertain what emotions one has, polygraph professionals are not able to do that either.

Polygraphy has also been faulted 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. However, CIA spy Harold James Nicholson failed his polygraph examinations, which aroused suspicions that led to his eventual arrest. Polygraph examination and background checks 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.

The polygraph also failed to catch Gary Ridgway, the "Green River Killer". Ridgway passed a polygraph in 1984 and confessed almost 20 years later when confronted with DNA evidence.

Conversely, innocent people have been known to fail polygraph tests. In Wichita, Kansas in 1986, after failing two polygraph tests (one police administered, the other given by an expert that he had hired), Bill Wegerle had to live under a cloud of suspicion of murdering his wife Vicki Wegerle, even though he was neither arrested nor convicted of her death. In March 2004, a letter was sent to The Wichita Eagle reporter Hurst Laviana that contained Vicki's drivers license and what first appeared to be crime scene photographs of her body. The photos had actually been taken by her true murderer, BTK, the serial killer that had plagued the people of Wichita since 1974 and had recently resurfaced in February 2004 after an apparent 25 year period of dormancy (he had actually killed three women between 1985 and 1991, including Wegerle). That effectively cleared Bill Wegerle of the murder of his wife. In 2005 conclusive DNA evidence, including DNA retrieved from under the fingernails of Vicki Wegerle, demonstrated that the BTK Killer was Dennis Rader.

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.

Law enforcement agencies and intelligence agencies in the United States are by far the biggest users of polygraph technology. In the United States alone all federal law enforcement agencies either employ their own polygraph examiners or use the services of examiners employed in other agencies. This is despite persistent claims of unreliability. For example in 1978 Richard Helms, the 8th Director of Central Intelligence, stated that:

"We discovered there were some Eastern Europeans who could defeat the polygraph at any time. Americans are not very good at it, because we are raised to tell the truth and when we lie it is easy to tell [we] are lying. But we find a lot of Europeans and Asiatics [who]
can handle that polygraph without a blip, and you know they are lying and you have evidence that they are lying."


Several countermeasures designed to pass polygraph tests have been described. 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."

Other suggestions for countermeasures include for the subject to mentally record the control and relevant questions as the examiner reviews them prior to commencing the interrogation. Once the interrogation begins, the subject is then supposed to carefully control their breathing during the relevant questions, and to try to artificially increase their heart rate during the control questions, such as by thinking of something scary or exciting or by pricking themselves with a pointed object concealed somewhere on their body. In this way the results will not show a significant reaction to any of the relevant questions.

2003 National Academy of Sciences report