Polygraph
A
polygraph (commonly and inaccurately referred to as a "
lie detector") is a device which measures and records several physiological variables such as
blood pressure,
heart rate,
respiration and
skin conductivity while a series of questions are being asked, in an attempt to detect
lies. The above measurements are posited to be indicators of anxiety that accompanies the telling of lies. Thus, measured anxiety is equated with telling untruths. However, if the subject exhibits anxiety for other reasons, a measured response can result in unreliable conclusions.
A polygraph test is also known as a
psychophysiological detection of deception (PDD) examination. The original polygraph was invented by
John A. Larson.
A typical polygraph starts with a pre-test interview designed to establish a connection (or find a
scientific control) between the tester and the testee and to gain some preliminary information which will later be used for "Control Questions " or C (see below). Then the tester will explain the polygraph, emphasizing that it can detect lies and that it is important to answer truthfully. Then a "stim test" is often conducted: the testee 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 ("Are you 35 years old?"), 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 R the polygrapher is really interested in. The different types of questions alternate. The test is passed if the physiological responses during the probable-lie control questions are larger than those during the relevant questions. If this is not the case, the tester attempts to elicit admissions during a post-test interview ("Your situation will only get worse if we don't clear this up").
While some people believe that polygraph tests are reliable, there is little scientific evidence to buttress this claim. For example, while some claim the test to be accurate in 70% - 90% of the cases, critics charge that rather than a "test", the method amounts to an inherently unstandardizable interrogation technique whose accuracy cannot be established. 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. It is interesting to note that, so far, no scientific study has been published that offer convincing evidence of the validity of the polygraph test. Polygraph tests have also been criticized for failing to trap known
spies such as
Aldrich Ames, who passed two polygraph tests while spying for the Russian government.
A study conducted by the National Academy of Sciences concluded that there is "little basis for the expectation that a polygraph test could have extremely high accuracy."[
1]
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. In an interview, Ames was asked how he passed the polygraph test. His response was that when told he was to be polygraphed he asked his Soviet handlers what to do, and was quite surprised that their advice was simply to relax when being asked questions, which he did.
While lie detector 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) [
2], the
US Supreme Court left it up to individual jurisdictions whether polygraph results could be admitted as evidence in court cases.
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 his testimony by submitting himself to a polygraph session.
In Canada, the use of a polygraph is sometimes employed in screening employees for government organizations. However, in the 1987 decision of
R. v. Béland, the
Supreme Court of Canada rejected the use of polygraph results as evidence in court.
According to
antipolygraph.org, a web site skeptical about the polygraph, the polygraph was used at a state facility attached to the Joliet Correctional Center to help decide whether to free offenders [
3].
Similar techniques were used in the ancient times. For instance, 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. In
Ancient China, during a
prosecutor's
speech the suspect held a handful of
rice in his or her
mouth. 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 remained dry.
*
Voice stress analysis*
Brain fingerprinting* Mikkelson, B. (2000).
http://www.snopes.com/legal/colander.htm, Snopes
* Roese, N. J., & Jamieson, D. W. (1993). Twenty years of bogus pipeline research: A critical review and meta-analysis.
Psychological Bulletin, 114, 363-375.
* Katherine Ramsland:
The Polygraph* George W. Maschke and Gino J. Scalabrini:
The Lie Behind the Lie Detector*
American Polygraph Association* A 2003 report by the
National Academy of Sciences found that polygraph testing lacks sufficient validity for use in employment prescreening, http://www.nap.edu/books/0309084369/html/
*
Polygraph examinations*
Polygraphs and the National Labs: Dangerous Ruse Undermines National Security*
wikiHow: How to Cheat a Polygraph Test
