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. One example of a failed polygraph includes the Green River Murder Case of 1982. A suspect named Melvin Foster allegedly failed a given lie detector test whereas another suspect, Gary Leon Ridgeway passed his. After nearly 20 years, DNA tests and a confession from Ridgeway proved Foster was innocent. 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 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.
In the high-profile disappearance of 7-year-old Danielle van Dam of San Diego in 2002, neighbor David Westerfield became the prime suspect when he failed his polygraph with a greater than 99% probability he was lying. But this claim has been challenged because the examiner kept the space heater on, making Westerfield uncomfortably hot; he constantly adjusted his machine, he said because the readings were too low; and he made a number of subtle changes to the questions he said he was going to ask, even though he said he wouldn’t. The examiner thought Westerfield’s alibi, a meandering weekend trip, was "as crazy as it gets"; he interviewed him for 3 hours, and at the end of the test, accused him of being involved in Danielle’s disappearance. Westerfield attributed his failing the test to his compassion for Danielle's family. In subsequent letters he said that, a couple of days later, they discovered that his test contained false results and they asked him to retake the test, but his attorney, who said it probably meant that the first test wasn’t set up right, wouldn’t allow it.
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 their 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 can handle that polygraph without a blip, and you know they are lying and you have evidence that they are lying."
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