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Lie Detectors Tell Lies : The Unreliability of Polygraphs Used in Criminal Trials and
Investigations
Polygraphs, commonly known as lie detector tests, are in question to whether or not they
are realiable enough to use in court cases. The common test used in criminal investigations is the
Control Question Test (CQT) . The CQT works by comparing physiological disturbances that
occur when questions are asked which are relative to the crime in question. Vague control
questions are asked to allow an innocent person to show more physiological disturbances to the
vague questions than to the questions which are directly relevant to the crime at hand. If the
person in question shows more disturbances when asked the relevant questions, it is a good
indication of deception (Honts 309). Even though courts and criminal investigators do permit
other unreliable evidence such as eyewitness testimonies, the polygraph is not reliable enough to
be allowed as evidence in the delicate process and evidence in criminal investigations.
Polygraphs can too easily be defeated by simple countermeasures to be accepted as
reliable and allowed in criminal investigations. Charles Honts , David Raskin, and John Kircher
from the Department of Psychology at the University of Utah state the following in their article
“Mental and Physical Countermeasures Reduce the Accuracy of Polygraph Tests”:
Research has shown that training in simple physical maneuvers, such as biting the
tongue or pressing the toes to the floor, can be effective in defeating polygraph
tests by enhancing physiological reactions to control questions. Honts, Hodes, and
Raskin reported that 60% of their decisions were incorrect when subjects had
been trained to unobtrusively bite their tongues and press their toes to the floor
when control questions were presented during the test. Using similar training and
stronger incentives to pass the test, Honts, Raskin, and Kircher failed to correctly
classify any subjects who were using countermeasures. (252)
This statement shows that the tests are not only unreliable when given by experts, but they are not
even correct half the time. The polygraph is not efficient enough to be correct during practice
tests, and the polygraph is definitely not efficient enough to be used as evidence in trials or as a
basis of guilt or innocence in criminal investigations.
Polygraphs are not accepted by the expert psychophysiological scientific community as a
sole determinant in a person’s innocence or guilt. In 1995, W.G. Iacono conducted a poll of
members of the Society for Psychophysiological Research, the same group that the Gallup poll
surveyed a decade earlier, and asked them what their opinion of the CQT polygraph test was.
The possible choices were the following : a sufficiently reliable method to be the sole determinant,
a useful diagnostic tool along with other evidence, of little usefulness when put up against other
types of evidence, and of no usefulness (427). The majority of the respondents chose the third
option, of little usefulness when put up against other types of evidence. This shows that experts
in the field where polygraphs originate from do not even believe that these tests are reliable.
There is no way that these tests are reliable enough to be presented as evidence in trials.
Polygraphs are unreliable to the point that they can incriminate innocent people. Michael
Phillips from the department of medicine at Sisters of Charity Health Care System states that “if
the polygraph were merely useless, it would not be so bad. Unfortunately, it is harmful because it
generates a large number of false-positive test results that may incriminate people who are telling
the truth” (413). Phillips also asks,”who would want to use a fire alarm or a cancer test that was
wrong 90% of the time” (413). This is very logical when put into simple terms. Since the
polygraph is unreliable to the extent of incriminating innocent people then all the test can do is
confuse matters even more. If innocent people are put in question there could be so many
suspects in a criminal trial that there would be more time spent on figuring out who the true
suspect is than time spent attempting to convict the suspect of his crime.
Some people question why polygraph evidence is not permitted in criminal trials and
investigations when other unreliable sources are allowed in courts as evidence. Donald Dripps
states that “courts routinely receive eyewitness testimony, handwriting analysis, and other
evidence of doubtful reliability.” “In United Stated v. Scheffer, the Supreme Court, by an 8-to-1
margin, upheld a Military Rule of Evidence that prohibits reception of polygraph evidence.”
“Justice John Paul Stevens, the lone dissenter, challenged each of these interests. Polygraph
evidence, the dissenting opinion maintains, is at least as reliable as much of the other evidence that
is routinely admitted, even if one accepts the estimates of reliability given by opponents of
polygraph evidence” (75). Other types of questionable evidence being admitted does not support
the argument of allowing polygraph evidence. Regardless of whether the other types of evidence
are reliable or not, polygraphs have been proven unreliable and should not be allowed as evidence
in trials or in criminal investigations. A system that is correct 50% of the time, at best, is not
reliable. This poor effeciency proves that polygraphs evidence should not be admitted in a court
of law.
An argument for polygraph testing as evidence is that it can immediately dismiss an
suspect who is innocent. If a guilty suspect knows the previously mentioned countermeasures to
polygraph testing then he or she can be presumed an innocent suspect by defeating the polygraph
test. This is the quickest way to let a criminal go free, not the quickest way to let an innocent
man go free. If this method was allowed for immediate liberation of an innocent suspect then
there would be many more innocent suspects called into question when the true criminal is let off
without question.
Another reason that some people believe that polygraph evidence should be allowed in
trials is that it gives a good indication to whether a suspect is guilty or innocent. Even though the
test is not always accurate, it can be useful in predicting a suspect’s guilt. A suspect’s guilt or
innocence is not something to toy with, and these less than perfect tests are doing just that. M.T.
Bradley says,”strong faith in the CQT seems unjustified. Reviews of field and laboratory work
have found actual polygraph accuracy to be substantially lower than the estimates of perfection or
near perfection given by field workers” (153). A field worker is more accurate than these tests.
This shows that bringing in the test is doing nothing but complicating the cases, and it causes the
court to second guess the field workers who have been proven more accurate than the tests.
Polygraphs are an inefficient way of proving someone’s guilt. If a method of determining
guilt and innocence is so unreliable, a suspect’s right to a fair trial is compromised when that
evidence is permitted to be used in a case. Until the reliability of polygraphs can be improved,
they should not be allowed as evidence in criminal trials and investigations.
Bibliography
Works Cited
Bradley, M.T., V.V. MacLauren, and S.B. Carle. “Deception and Nondeception in Guilty
Knowledge and Guilty Actions Tests.” Journal of Applied Psychology. April 1996 :
153-160.
Dripps, Donald A. “Polygraph Evidence After United States v. Scheffer.” Trial June 1998 :
75-76.
Honts, Charles R. “Criterion Development and Validity of the CQT in Field Application.”
Journal of General Psychology. October 1996 : 309-324.
Honts, Charles R., David C. Raskin, and John C. Kircher. “Mental and Physical Countermeasures
Reduce the Accuracy of Polygraph Tests.” Journal of Applied Psychology April 1994 :
252-259.
Iacono, W.G., and D.T. Lykken. “The Validity of the Lie Detector : Two Surveys of Scientific
Opinion.” Journal of Applied Psychology June 1997 : 426-433.
Phillips, Michael. “Problems with the Polygraph.” Science 15 Oct. 1999 : 413.
Word Count: 1185
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