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Controversies: Polygraph Evidence in Court

About the controversies series: Controversies publications present the academic literature pertaining to an issue, and take one empirically-based side. These publications are intended for distribution and are extremely useful for academics, professionals or laypeople who are interested in issues in psychology and law. They provide a means to disseminate empirically based information in a way that is both quick and useful. Controversies publications undergo the EAPL-S peer review process and editing before publication.

About the author: This article was written by Leandro Velasco, M.A., LPA. Leandro is a licensed psychological associate and currently working towards certification as a behaviour analyst (BCBA) at the University of North Texas.

View this document in it's full glory by downloading the pdf here.

Remember to also read our fact sheets on deception detection, and forensic neuropsych!


Our ability to detect deception, and in turn, the absence of deception, poses significant challenges to modern-day judicial systems, businesses, and state and federal authorities. The judicial, economic, and national security implications of reliably detecting deception place the polygraph under significant scrutiny. Because of the general awareness and administration of the polygraph across various fields, it will be discussed in this article. Television and movies may also contribute to the misunderstanding among the general public as to what the polygraph is purported to measure. The modern polygraph measures physiological response (such as respiration and pulse rates) as a subject is questioned by an interrogator [8]. However, as will be discussed in this publication, these variables may be influenced by other factors.

“The polygraph does not detect lies, but instead measures physiological responses postulated to be associated with deception. None of these responses are specific to deception, nor are they necessarily always present when deception occurs” – Grubin & Madesen [4]

Evidence for.

Several federal agencies within the US use the polygraph as a means to identify potential deception among would-be applicants and employees [10, 4]. However, admissibility as evidence in a trial and its use as an applicant and employee screening-tool have two very different consequences. It does reflect that within certain circles and professional organizations, the polygraph is considered sufficiently reliable and valid for its use within a particular context. In the US, the standards of admissibility of scientific evidence, such as the polygraph, have been heavily influenced by the Frye (1923) and Daubert (1993) decisions. Daubert encompasses considerations that judges should apply in determining whether to admit expert testimony that is based on scientific evidence: (a) testability (or falsifiability), (b) error rate, (c) peer review and publication, and (d) general acceptance. While this is does not reflect widespread consensus across jurisdictions, it does indicate that the polygraph passed the Daubert criteria for scientific evidence. This is clear when we note in 19 out of 50 states in the US polygraph results are admissible as evidence in court [4].

Evidence against.

Concern has been expressed regarding the use of the polygraph based on the lack of standardized testing procedures, the unreliable error rate, and the lack of general scientific acceptance [10]. With respect to the polygraph, the potential source of observed variance may come from potential medical and neurological conditions that were present during the administration [2]. Any number of prescribed medical and/or psychotropic medications may affect how the individual will respond physiologically to questioning. Potential counter-measures also appear to be somewhat effective in confounding measurements from the polygraph. For example, the use of physical, mental, and pharmacological counter-measures, in tandem, have been at least moderately effective in obtaining either a false-negative or inconclusive result [5]. Lastly, generalizable scientific research on the polygraph may be hard to obtain, because the psychological and physiological stressors that someone accused of a crime would go through cannot be easily replicated in a controlled laboratory setting [6].

What it all means.

The use of the polygraph within different environments, contexts, and situations has been sanctioned by government bodies and judicial systems across various countries. In terms of detecting deception or the lack-there-of, there appears to be no other viable alternative to the polygraph that would bring about a more satisfactory, if not reliable, measurement of deception. Nonetheless the ramifications of obtaining false-positives and false-negatives may have significant implications within criminal proceedings, employment opportunities, and national security.

At present, there does not appear to be sufficient consensus within the US and UK judicial system, as well as their respective psychological organizations, as to how accurate and reliable the polygraph is and should be [8]. The need for standardized practice, methodology, training, and oversight by an organized body (with authority to regulate its use) leaves it susceptible to misuse and misunderstanding by both the public and private sectors.

The quote wall.

“At a minimum, we need to continue to be wary about the claimed validity of the polygraph as a scientific tool, especially with regard to its current forensic uses.”

– Cited from an academic article written by Dr. Faigman, a distinguished researcher in the area of legal policy, Dr. Fienberg, a statistics and psychology, and Dr. Stern, an expert on the poloygraph.

"The idea that we can detect a person's veracity by monitoring psychophysiological changes is more myth than reality. For now, although the idea of a lie detector may be comforting, the most practical advice is to remain skeptical about any conclusion wrung from a polygraph.”

- A statement from the American Psychological Association that summarizes the standing of the current research on the polygraph.

“A more appropriate role for the polygraph device is as an investigative tool. In this way, investigators can develop leads and acquire various avenues of approach to facilitate fact-finding investigations.

– David Gallai, J.D., takes a legal perspective on polygraph as an investigative tool.

“Theoretically, delusions and other impairments in reality testing that are indistinguishable from the truth on a cognitive level could be inaccessible to either the polygraph or brain-imaging based lie-detection.”

– Dr. Daniel D. Langleben, and his colleagues, discusses the feasibility of physiological lie detectors.

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  1. American Psychological Association (2004). The truth about lie detectors (aka Polygraph tests). Retrieved from: www.apa.org/research
  2. Faigman, D, L., Fienberg, S. E., Stern, P. C. (2003). The Limits of the polygraph. Issues in Science & Technology. 20, 40-46.
  3. Gallai, David. (1999). Polygraph evidence: Should it be admissible? American Criminal Law Review, 36, 87-116.
  4. Grubin, D., & Madsen, L. (2005). Lie detection and the polygraph: A historical review. The Journal of Forensic Psychiatry & Psychology. 16, 357-369.
  5. Gudjonsson, G.H. (1988). How to defeat the polygraph tests. In A. Gale (Ed.), The Polygraph test: Lies, trust and science (pp. 126-136). London: Sage.
  6. Krapohl, D. J. (2011). Limitations of the Concealed Information Test in criminal cases. In B. Verschuere, G. Ben-Shakhar, E. Meijer (Eds.) , Memory detection: Theory and application of the Concealed Information Test (pp. 151-170). New York, NY US: Cambridge University Press.
  7. Langleben, D. D., Dattilio, F. M., Guthel, T. G. (2006). True lies: Delusions and lie-detection technology.  Journal of Psychiatry & Law. 34, 351-370.
  8. Melton, G. B., Petrila, J., Poythress, N. G., & Slobogin, C. (2007). Psychological evaluations for the courts: A handbook for mental health professionals and lawyers (3rd ed.). NewYork, NY: Guilford Press.
  9. Sake, L. & Gershon Ben-Shakhar. (1999). Admissibility of polygraph tests: The application of scientific standards post-Daubert. Psychology, Public Policy, and Law, 5, 203-223.
  10. Wrightsman, L. S. (2001). Forensic psychology. Belmont, CA: Wadsworth.

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