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Leonarde Keeler, one of the inventors of the polygraph, testing his polygraph on a subject
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A polygraph is a machine, or a test using said machine, which measures the changes in a person's body, such as pulse, breathing rate, and skin temperature. It is used as a lie detection test. It is based on the principle that when lying, one will become nervous and have an increased pulse and need for air. However, its effectiveness is very limited and the test often leads to inconclusive or incorrect results.

Validity of a polygraph[edit]

The polygraphy works by measuring some physiological responses to questions. The method involves establishing a "baseline" by measuring a subject's responses to certain undramatic and nonthreatening questions. Following this, the interview will take place and the measurements will be compared with this baseline. So from the method alone, it can be seen that the polygraph isn't so much a "lie detector" (as it is commonly portrayed) but just a system to measure someone's emotional state — the theory is that if someone lies, their emotional state will change. The method alone should suggest how people can produce false results or intentionally game the system in their favour. Sociopaths,[1] for example, have a nervous system that responds differently: when they lie, they remain as cool as the proverbial cucumber.[2] One in twenty-five people are sociopaths.[2] However, the ubiquity of the "lie detector" means that it has been thoroughly studied, and rarely (even when used properly by trained individuals) produces favourable results. Many pieces of research show that either a polygraph is not a valid tool for use in courts,[3] or that the validity is unmeasureable.[4]

In short, just because someone is nervous doesn't mean they're lying, and just because someone is overconfident doesn't mean they're telling the truth. Moreover, people with anxiety disorders (such as social anxiety disorder or PTSD) may very well "fail" the polygraph due to being stressed and triggered during the test.

In 2002 the American Academy of Sciences called the Polygraph "a danger to national security"[5], while John T Capiocco's Handbook of Psychophysiology states that "no spy has ever been identified as a result of a polygraph test".[6] That statement technically isn't true, as the CIA did detect that Harold James Nicholson was spying due to a "failed" polygraph, but others weren't. In fact, Aldrich Ames (who was responsible for the deaths of at least ten American agents) "passed" two polygraphs.

Ways a polygraph test can give wrong results[edit]

If the simple act of taking a polygraph test makes a subject nervous then it will be difficult for the "baseline" to be established. This makes the readings during the real section of the interview almost impossible and this leads to "inconclusive" results. Although inconclusive results should be taken as just that, inconclusive, and therefore should be ignored, they may be interpreted as a sign of guilt — on the principle that honest and innocent people shouldn't be fearful of lie detector tests. However, this is wrong; the situation of taking "lie detector" tests is harrowing for many. Indeed, an honest person who is aware of the limitations of a polygraph may be even more nervous, since they may have a strong fear of false positives, leading to a self-fulfilling prophecy.

If a particular question makes the subject nervous, even as they give the correct, or honest, response, the test will give a "false" reading. In fact, one televised use of the polygraph for demonstration purposes showed the strongest reaction to the interviewer saying "now I'm going to ask you an intimate and personal question;" although a question of that nature was never asked, the mere thought of a harassing question sent the measurements quite wild.

It is important to note that most effects that cause the polygraph to be unreliable are invariant of whether a person is innocent or guilty, lying or telling the truth, intentionally trying to produce haphazard results or not.

Ways to "cheat" on a polygraph test[edit]

There are a few ways a polygraph can be "cheated". Not all of them are intentional.

  • If the subject doesn't realize they aren't telling the truth
  • If the subject doesn't naturally become nervous when lying (alternatively, becoming naturally nervous at everything works too: that corrupts the baseline)
  • If the subject trains themselves to remain calm while lying
  • If the subject simulates the physiological signals of lying when the questioner is establishing the baseline.

The last two are important as people can, and do, learn to do this knowing that they may be subject to a polygraph at some point. Before the actual questioning session begins, the polygraph technician leads the subject through a "pre-test" session. During this session, the technician asks the subject to answer a set of questions. The subject is asked to answer some questions truthfully, then lie when answering other questions. The technician then adjusts the polygraph to compensate for certain nervous reactions that the subject may have. Therefore intentionally cheating usually involves basically fooling around with this "pre-test" session.

To reduce the polygraph's reaction to nervousness — or lying — all the subject has to do is increase their nervousness during the truthful-answers portion of the pre-test. Among the more popular methods are:

  • Bite the side of your tongue
  • Tightly curl your toes
  • Count backwards from 10 to 1
  • Flex the anal sphincter [7]

The subject must wait until the technician asks the question before doing any of these.[8]

Polygraph Technician Training[edit]

About 15 weeks, with regular reclassification seminars. Just Google "Polygraph Training" and you'll find many training programs. None are properly accredited, of course. For comparison, it often takes six months to train to become a barber.

Use of polygraphs in a court of law[edit]

Currently, there is no US Supreme Court ruling of the admissibility of a polygraph for all cases. However, in Frye vs. the United States, the Supreme Court upheld a ruling denying the use of a polygraph as evidence in the case of Frye. The ruling included these words:

"Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs." [9]

However this ruling is from 1923. In the United Kingdom and in Ontario, Canada, polygraph evidence is inadmissible in a criminal court. Polygraph tests are inadmissible in most U.S. states in criminal prosecutions; some allow their admission if both the prosecution and the defense agree to it.[10]

Use in employment[edit]

In the United States most private sector employees can not be forced to submit to a polygraph thanks to the Employee Polygraph Protection Act of 1988.Wikipedia[11] In the private sector exceptions remain for people in security and certain pharmaceutical professions. The law does not cover government employees. Polygraphs remain in use largely in pre-screening for law enforcement and jobs in the intelligence community. Agencies can require that certain very high level security clearance applicants undergo a polygraph.[12]

In the case of US intelligence communities they have effectively acknowledged the polygraph is not a viable truth telling technique. Despite this they have chosen to continue requiring polygraphs for the simple reason that people keep revealing things during a polygraph that they otherwise wouldn't. In other words it's proven an effective psychological manipulation tool for tricking those who don't understand the limits of polygraphs into giving up secrets. One can argue that engaging in psychological manipulation of your employees before they have even started their jobs is a bit harsh, but at least the government does have a justification for using pseudoscience this one time.[citation needed]

Use of polygraphs in popular entertainment[edit]

The entertainment industry is run by people who will believe almost anything[note 1] for people who will believe almost anything,[note 2] and even when they don't, many of them prefer entertainment over truth in their fiction. So naturally, the polygraph is a popular device on television, on stage, and in the movies. With the exception of police procedurals that portray the use of polygraphs,[note 3] some of the more famous examples of polygraphs in entertainment are:

"Nada más que la verdad", a.k.a. "The Moment of Truth"[edit]

Nada más que la verdad[13] ("Nothing But the Truth") was a Colombian TV game show series created by American TV producer Howard Schultz, owner of the ironically named production company "Lighthearted Entertainment." As of 2009, versions of this show have been produced in at least 46 countries. Currently, it is the most notorious of all "entertainments" that use polygraphs.

The game consists of a contestant who is connected to a polygraph and asked a minimum of fifty yes-or-no questions. The contestant is then brought onstage. Nearby are three or four of the contestant's friends and/or family members. Twenty-one of the questions from backstage are again asked of the contestant. If any of the questions are deemed to be too sensitive by one of the contestant's friends or family, they can hit a button that prevents the contestant from answering. This option can only be used once for each contestant. A replacement question, which may be even more sensitive, is then asked in its place. If the onstage answer matches the "true" answer from the backstage polygraph, the contestant is allowed to go on or quit. If the onstage answer is considered "false"[note 4] when compared to the backstage polygraph, the contestant loses the game and loses any money "earned" up to that point.

It should be pointed out that putting someone into a high stakes situation with family and friends watching as you're asked offensive questions that likely concern them is a recipe for a contestant to feel fear, apprehension, anger, or uncertainty whether or not you are lying, all these emotions result in the physiological symptoms the polygraph is testing for. In other words, the contestants are already primed in such a way that they are likely to give responses that look like a lie on a polygraph whether or not they are actually lying. No doubt those running the show know this and consider it a feature, not a bug; after all, a show is far more interesting when a contestant is called out for an embarrassing 'lie'; who cares if it's really a lie or not if it makes for entertaining television? Any resulting trouble with family and friends who believe the polygraph's accuracy and are angered by the supposed lie don't really matter as long as you get ratings.

There have been many controversies connected to this show. The original Colombian version was cancelled when a woman was asked if she had hired a hit man to kill her husband. When she answered "yes," her husband fled.

The American version, titled The Moment of Truth,[14] ran on Fox[note 5] during 2008 and 2009. While nobody admitted to anything as spectacular as a murder-for-hire plot, there were other questionable instances.

  • One contestant lost when his "no" answer to the question "When you were a male model, did you stuff your underwear?" was deemed false. His look of utter shock may have been the most honest moment of the series.
  • Another contestant had been accused by his ex-wife of gambling away his son's college fund.[note 6] He "truthfully" denied stealing his son's college fund. When he and his son embraced, his son said something (barely audible) to the effect of how he knew he shouldn't have believed his mother.[note 7]
  • Another contestant admitted to having affairs in front of her husband, who was present onstage. While many pundits and social critics focused on the effect this had on her husband,[15] they seemed to ignore what was happening to her father, who was also present onstage. Some of the questions she answered seemed designed to exact revenge on her father,[note 8] not her husband.[note 9] She was eventually tripped up when her "yes" answer to the question "Do you think you're a good person?" was deemed "untruthful." According to host Mark L. Wahlberg, the episode barely got the OK to air.[note 10] This was the most-discussed episode of the U.S. series.
  • The only person ever to win the top prize was a woman raised in a polygamist religious community whose $500,000 question was asking if her father had ever committed statutory rape, which she replied in the affirmative, resulting in the first grand prize win in the history of game shows where absolutely no one seemed happy. Unlike the above examples, this episode was never aired by Fox.[16]
  • Travis Walton appeared on an episode late in the series' run, where he was eliminated on a question asking him if he really was abducted by a UFO, where his answer of "yes" was deemed "untruthful". His episode was also never aired by Fox.
  • Only a few of the contestants successfully completed the third tier ($100,000 level) of the U.S. show. Only two contestants completed the fourth tier ($200,000). Only one made it to the fifth tier ($350,000) and sixth and final tier ($500,000).[17] Jeez, what gives?! Even Who Wants to be a Millionaire? has given away a million now and then!

Computer voice stress analysis[edit]

In an attempt to come up with a super duper computer polygraph-type device, NITV Federal Services created the Computer Voice Stress Analyzer,[18] a device that purports to detect inaudible-to-human stress in voice recordings, and then makes the additional leap of faith that stress equals deceit.

A 2003 study by the US National Research Council concluded, "Overall, this research and the few controlled tests conducted over the past decade offer little or no scientific basis for the use of the computer voice stress analyzer or similar voice measurement instruments as an alternative to the polygraph for the detection of deception."[19]:168

A 2008 review by the US National Institute of Justice found that voice stress analyzers they had only a 50% accuracy rate, i.e., the same as chance.[20]

A 2013 conference paper concluded that there was "scientific implausibility" of the working principles of companies engaged in manufacturing voice stress analysis devices, and that the companies engaged in "aggressive propaganda".[21]

Despite these severe underlying problems with the technology, according to NITV, there are more that 3000 agencies that use this technology.[22]

NITV has been pissed at Wikipedia for allowing the "hijacking" of their industry's Wikipedia page (Voice stress analysisWikipedia) and reporting independent studies.[23]

See also[edit]

External links[edit]


  1. Scientology, anyone?
  2. 2012 apocalypse anyone?
  3. Too many to list.
  4. Polygraph operators hedge their judgements on "true" or "false" answers. They usually say that the "response" was "truthful" or "deceptive."
  5. Where else?
  6. Just for the record, this contestant is a wannabe professional actor who is employed at a major horse track. In his third question, he admitted to being a gambling addict. He admitted to being a Hair Club for Men member. (No surprise there. The rug he wore looked like a castoff from The Sopranos makeup trailer.) Next, when he was asked if he had a bank account his live-in girlfriend was unaware of, he paused for what seemed like an eternity, then "truthfully" answered "no." And, unlike the guy mentioned above, he admitted to stuffing his shorts. Throughout the taping, he exhibited an over-the-top glibness that most two-year-olds would say was phony. He even threw kisses at his son and girlfriend. All of this should scream "don't trust him!" How accurate are polygraphs again?
  7. All of the questions were supplied by the friends and family members present onstage. Therefore, the girlfriend suspected this contestant of having a secret bank account and the son believed that he gambled away his college funds.
  8. Her ex-boyfriend came onstage to ask if she would leave her husband to be with him. Her sister hit the "don't answer" button. For the replacement question, the ex-boyfriend asked if she thought that they were meant to be together. She answered "yes." Her father was visibly pissed from the moment her ex-boyfriend walked onstage.
  9. Who later admitted to knowing about the affairs. He later filed for divorce when other affairs came to his attention.
  10. Wow! Fox has standards. Oh, wait. It aired. Never mind.


  1. http://www.mcafee.cc/Bin/sb.html
  2. 2.0 2.1 Anscombe, Roderick. Spot the liar. When the art of the question meets the art of the lie. Retrieved 7 November 2009.
  3. The polygraph in doubt. APA online.
  4. Scientific Validity of Polygraph Testing: A Research Review and Evaluation
  5. Moment of truth as lie detector's worth comes into question
  6. John T Capiocco. Handbook of Psychophysiology. (Cambridge university Press (2007). ISBN 0521844711.), p. 691 Google book search result
  7. QI Transcript: Series 5, Episode 7.

    Sweat, palpitations, vibrations in the body and various clenchings of muscles and so on. But in order to see how it works, you obviously have to ask people a series of questions to which they don't lie, like their name and their address. These are called control questions. So if you want to beat it, when you're being asked what your name is, sort of behave as if you were lying. In other words, either think very exciting thoughts or clench your anal sphincter.

  8. "Lie Detector Tests: The Truth About Polygraphs" UK-Skeptics Website
  9. http://law.jrank.org/pages/12871/Frye-v-United-States.html
  10. C. J. S. Crim. Law § 1037
  11. https://www.dol.gov/whd/polygraph/
  12. https://news.clearancejobs.com/2011/06/06/how-to-prepare-for-a-security-clearance-polygraph-examination/
  13. See the Wikipedia article on Nada más que la verdad.
  14. See the Wikipedia article on The Moment of Truth (U.S. game show).
  15. The Moment of Truth turns into a time of pain" Los Angeles Times "Show Tracker" website, 27 February 2008, accessed 6 November 2009.
  16. “The Moment of Truth” Produces the Most Awkward Jackpot Win Ever by Alex Davis (24 Jun 2001) Buzzerblog (archived from September 8, 2012).
  17. See the Wikipedia article on List of The Moment of Truth episodes.
  18. Computer Voice Stress Analyzer NITV Federal Services.
  19. The Polygraph and Lie Detection (2003) The National Academies Press. doi:10.17226/10420. ISBN 9780309263924.
  20. Voice Stress Analysis: Only 15 Percent of Lies About Drug Use Detected in Field Test by Kelly R. Damphousse (March 16, 2008) National Institute of Justice.
  21. Voice stress analyses: Science and pseudoscience by Francisco Lacerda (2013) Proceedings of Meetings on Acoustics 19(1). doi:10.1121/1.4799435.
  22. ‘It’s like saying a Ouija board or an astrological chart is an investigative tool’: Law enforcement's unreliable tech by Susie Neilson & Matthias Gafni (June 4, 2024) San Francisco Chronicle.
  23. Wikipedia Alert — VSA Article Hijacked NITV Federal Services.