A polygraph, often incorrectly referred to as a lie detector, is a device that measures and records several clinical biomarkers, such as blood pressure, pulse, respiratory rate, and skin conductivity, and it is used while a person answers a series of questions to purportedly detect lies. Polygraphic assessments rely on the discredited assumption that some physiological mechanisms or functional state, and their variations thereof, could reliably account for psychophysiological phenomena supposedly invoked by (the act of) lying, though polygraphy is considered pseudoscience by the scientific community.
The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers; however, there are no specific physiological reactions associated with lying, making it difficult to identify factors that separate those who are lying from those who are telling the truth. In some countries, polygraphs are used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. Some United States law enforcement and federal government agencies, as well as many police departments, 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 examination".
Assessments of polygraphy by scientific and government bodies generally suggest that polygraphs are highly inaccurate, may easily be defeated by countermeasures, and are an imperfect or invalid means of assessing truthfulness. A comprehensive 2003 review by the National Academy of Sciences of existing research concluded that there was "little basis for the expectation that a polygraph test could have extremely high accuracy", while the American Psychological Association has stated that "most psychologists agree that there is little evidence that polygraph tests can accurately detect lies." For this reason, the use of polygraphs to detect lies is considered a form of either pseudoscience or junk science.
Testing procedure
The examiner typically begins polygraph test sessions with a pre-test interview to gain some preliminary information which will later be used to develop diagnostic questions. 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. Guilty subjects are likely to become more anxious when they are reminded of the test's validity. However, there are risks of innocent subjects being equally or more anxious than the guilty. Then the actual test starts. Some of the questions asked are "irrelevant" ("Is your name Fred?"), others are "diagnostic" questions, and the remainder are the "relevant questions" that the tester is really interested in. The different types of questions alternate. The test is passed if the physiological responses to the diagnostic questions are larger than those during the relevant questions.
Criticisms have been given regarding the validity of the administration of the Control Question Technique. 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 administering the questions.
An alternative is the Guilty Knowledge Test (GKT), or the Concealed Information Test, which is used in Japan. 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.For more info on the Guilty Knowledge Test, see The Guilty Knowledge Test (GKT) as an Application of Psychophysiology: Future Prospects and Obstacles
Effectiveness Assessments of polygraphy by scientific and government bodies generally suggest that polygraphs are inaccurate, may be defeated by countermeasures, and are an imperfect or invalid means of assessing truthfulness. Despite claims that polygraph tests are between 80% and 90% accurate by advocates, the National Research Council has found no evidence of effectiveness. In particular, studies have indicated that the relevant–irrelevant questioning technique is not ideal, as many innocent subjects exert a heightened physiological reaction to the crime-relevant questions. The American Psychological Association states "Most psychologists agree that there is little evidence that polygraph tests can accurately detect lies."
In 2002, a review by the National Research Council found that, in populations "untrained in countermeasures, specific-incident polygraph tests can discriminate lying from truth telling at rates well above chance, though well below perfection". The review also warns against generalization from these findings to justify the use of polygraphs—"polygraph accuracy for screening purposes is almost certainly lower than what can be achieved by specific-incident polygraph tests in the field"—and notes some examinees may be able to take countermeasures to produce deceptive results.National Research Council (2003); Pages 4 - 5
In the 1998 US Supreme Court case United States v. Scheffer, the majority stated that "There is simply no consensus that polygraph evidence is reliable [...] 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." The Supreme Court summarized their findings by stating that the use of polygraph was "little better than could be obtained by the toss of a coin." In 2005, the 11th Circuit Court of Appeals stated that "polygraphy did not enjoy general acceptance from the scientific community". [PDF] In 2001, William Iacono, Professor of Psychology and Neuroscience at the University of Minnesota, concluded: 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.
Polygraphs measure arousal, which can be affected by anxiety, anxiety disorders such as post-traumatic stress disorder (PTSD), nervousness, fear, confusion, hypoglycemia, psychosis, depression, substance-induced states (nicotine, stimulants), substance-withdrawal state (alcohol withdrawal) or other emotions; polygraphs do not measure "lies". A polygraph cannot differentiate anxiety caused by dishonesty and anxiety caused by something else.
Since the polygraph does not measure lying, the Silent Talker Lie Detector inventors expected that adding a camera to film microexpressions would improve the accuracy of the evaluators. This did not happen in practice according to an article in the Intercept.
US Congress Office of Technology Assessment In 1983, the US Congress Office of Technology Assessment published a review of the technology and found that
National Academy of Sciences In 2003, the National Academy of Sciences (NAS) issued a report entitled "The Polygraph and Lie Detection". The NAS found that "overall, the evidence is scanty and scientifically weak", concluding that 57 of the approximately 80 research studies that the American Polygraph Association relied on to reach their conclusions were significantly flawed.National Research Council (2013); Chapter 8: Conclusions and Recommendations, p. 212) These studies did show that specific-incident polygraph testing, in a person untrained in counter-measures, could discern the truth at "a level greater than chance, yet short of perfection". However, due to several flaws, the levels of accuracy shown in these studies "are almost certainly higher than actual polygraph accuracy of specific-incident testing in the field". By adding a camera, the Silent Talker Lie Detector attempted to give more data to the evaluator by providing information about microexpressions. However adding the Silent Talker camera did not improve lie detection and was very expensive and cumbersome to include according to an article in the Intercept.
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." 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". Similarly, a report to Congress by the Moynihan Commission on Government Secrecy concluded that "The few Government-sponsored scientific research reports on polygraph validity (as opposed to its utility), especially those focusing on the screening of applicants for employment, indicate that the polygraph is neither scientifically valid nor especially effective beyond its ability to generate admissions".IV Personnel Security: Protection Through Detection quoting Ralph M. Carney, SSBI Source Yield: An Examination of Sources Contacted During the SSBI (Monterey: Defense Personnel Security Research Center, 1996), 6, affirming that in 81% of cases, the derogatory informations were obtained through questionnaire and/or interrogation.
Despite the NAS finding of a "high rate of false positives," failures to expose individuals such as Aldrich Ames and Larry Wu-Tai Chin, and other inabilities to show a scientific justification for the use of the polygraph, it continues to be employed.
Countermeasures