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Date: June 10, 1997
Contact: Pam Willenz
Public Affairs Office
(202) 336-5707
Email: public.affairs@apa.org

Psychologists Surveyed On Lie Detectors Say Most Are Not Valid

Not Scientifically Sound and Can Be Easily Deceived

WASHINGTON -- The use of the polygraph (lie detector test) is not nearly as valid as some say and can easily be beaten and should never be admitted into evidence in courts of law, say psychologists from two scientific communities who were surveyed on the validity of polygraphs. This survey appears in the June issue of the American Psychological Association's (APA) Journal of Applied Psychology.

To obtain a scientific opinion on lie detector tests, members of the Society for Psychophysiological Research (SPR) and Fellows of the APA's Division of General Psychology were asked how accurate three different polygraphs were in detecting deception techniques.

The Control Question Test (CQT) 'compares the physiological disturbance caused by relevant questions about the crime (O.J.Simpson Case: 'On June 12, did you stab your ex-wife, Nicole?') with the disturbance caused by questions relating to possible prior misdeeds ('Before 1992, did you ever lie to get out of trouble?'),' said co-authors W.G. Iacono, Ph.D., and D.T. Lykken, Ph.D., from the University of Minnesota at Twin Cities. This test is often used to determine whether certain criminal suspects should be prosecuted or classified as uninvolved in the crime.

The Directed Lie Test (DLT) detects lying by differentiating how a person reacts when they are told to deliberately lie and how they react when they tell the truth. The Guilty Knowledge Test (GKT) 'attempts to detect whether a suspect has knowledge that only the person who committed the crime and the police would have,' said Dr. Iacono.

A total of 421 psychologists with expertise in psychophysiology and statistics responded to two survey questions.The survey results found that psychologists and psychophysiologists doubted the accuracy claims that have been made by the polygraph community.

Would You Say that the CQT, GKT, DLT is based on scientifically sound psychological principle or theory?

CQT Of 84% responding
36% said yes
Of 84% responding
30% said yes
GK Of 83% responding
77% said yes
Of 81% responding
72% said yes
DLT Didn't respond Of 89% responding
22% said yes

Would You Advocate that Courts Admit into Evidence the Outcome of Control Question Polygraph Tests?

Deceptive Of 91% responding
24% said yes
Of 95% responding
20% said yes
Truthful Of 91% responding
27% said yes
Of 96% responding
24% said yes

'Three-fourths of the psychophysiologists surveyed thought it unlikely that the validity of CQT could be as high as 85 percent,and the psychologists estimated its average validity at about 61 percent,' said the authors. 'Both groups felt strongly that the CQT results should not be admitted as evidence in court. However,almost three-fourths of both groups viewed the GKT as scientifically sound. But even though the GKT is seen as a promising forensic tool, we would not advocate its admissibility in the absence of additional research with real-life criminal cases.'Only the psychologists were asked about the scientific soundness of the DLT, and only 22 percent thought it was sound.

Article: 'The Validity of the Lie Detector: Two Surveys of Scientific Opinion,' by W.G. Iacono, Ph.D., and D.T. Lykken, Ph.D.,University of Minnesota, Twin Cities, in Journal of Applied Psychology, Vol.82, No. 3.

Dr. W.G. Iacono, Ph.D., can be reached at wiacono@tfs.psych.umn.edu

The American Psychological Association (APA), in Washington, DC, is the largest scientific and professional organization representing psychology in the United States and is the world's largest association of psychologists. APA's membership includes more than 151,000 researchers, educators, clinicians, consultants and students. Through its divisions in 50 subfields of psychology and affiliations with 58 state, territorial and Canadian provincial associations, APA works to advance psychology as a science, as a profession and as a means of promoting human welfare.

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