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A Case Against Polygraph Evidence Admissibility in Court Essay

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Updated: Dec 4th, 2019


The survival of any civilization depends on the establishment of laws of conduct and the following of the same by all the members of the society. Even so, not all members of the society follow the law on their own accord and as such, there is need for a Justice System which serves both as an instrument for retribution and deterrence.

There are two prominent agents employed by the criminal justice system. They are: police officers who are charged with enforcement of the criminal laws and prevention of crime in their respective jurisdictions and the court systems which play a vital role by administering justice. Courts are charged with ensuring that the criminal justice process runs its course from the arrest stage through to the sentencing.

The efficiency of the criminal justice system of a country has huge significance since a nation’s justice system has a direct bearing on the perceived legitimacy of a government by its people. As such, governments are always looking for ways to make the system more effective by increasing its accuracy rates. One of the means proposed for increasing the accuracy of the investigative process in crime fighting is the use of polygraph tests.

This device has captured the imagination of the nation and some courts have considered making evidence from polygraph tests admissible to court. This paper argues that polygraph evidence should not be admissible in federal courts due to the low accuracy levels of the test. The paper shall reinforce this claim by use of empirical literature that analyses the accuracy of the polygraph in lie detection.

Assumptions Underlying Polygraph Use

The polygraph test was invented by John Reid and the most widely used format is known as the comparison question test (CQT). CQT is generally applicable in criminal investigations as well as security screening by federal actors (Ben-Shakhar, 2002). Polygraph specialists argue that deception can be detected through the use of a science oriented interview technique which is known as “polygraphic examination”.

The fundamental assumption in polygraph tests is that “polygrapher can detect deception in an individual by assessing his/her physiological reactions to questions relating to the crime or other critical events of interest” (Furedy & Heslegrave, 1991, p.58). The important part of the polygraph test is the recording and measuring of the subtle changes in physiological functions that occur when a person lies.

The assumption here is that this physiological reactions are involuntary meaning that people are neither aware of the apparent changes and not can they reproduce them at will if they wanted to.

The physiological measures that are recorded in a polygraph examination are typically respiration, heart beat, blood pressure and sweating. The records are taken continuously as the subject is asked a series of questions that are related to the matter under investigation.

Bell and Grubin (2010) reveal that in the CQT, the basic assumption is that the innocent examinee will exhibit higher physiological arousal to the comparison questions about past misdeeds as compared to questions about the incident which is currently under investigation. On the other hand, the guilty examinee will exhibit higher arousal to questions about the incident that is the basis of the current investigation. Strong physiological reactions to the relevant questions are marked out to indicate deception on the part of the subject.

There are also some assumptions which are taken when interpreting the polygraph tests. To begin with, it is assumed that innocent participants will be more aroused by questions concerning comparison items. Several authors have questioned this assumption since it is also highly likely that the relevant item may be of strong concern to the innocent subject as well (Bell & Grubin, 2010; Fiedler, Schmid, & Stahl, 2002; Furedy, 1996; Iacono, 2000; Lykken, 1983).

Many critics of CQT point out that there is no explainable reason why physiological activity should increase or decrease when a person tells the truth. This rationale is more of an assumption than a fact that can be demonstrated.

Accuracy of the Polygraph

The accuracy of the polygraph test is not absolute and a recent review on the accuracy rates of what was considered high-quality laboratory studies indicated that for guilty subjects, the accuracy ranged from 53% to 100% while for innocent subjects, the accuracy ranged between 75% and 90% (Raskin & Honts, 2002). The findings from this study concluded that specific-incident polygraph tests (which is what investigators use) result in detection rates that are higher than chance but significantly less than perfect.

Another issue concerning polygraph test accuracy is the lack of standardization. This presents a major hindrance to asserting the validity of the CQT is that there is no standardized manner of administering the test. In the specific incident polygraph test, the analyzer is required to come up with the interview questions that will be used in the test.

The questions have a huge bearing on the accuracy of results as studies reveal that well structured questions increase accuracy while poorly structured questions decrease accuracy rates (Grubin & Bell, 2010). Due to this lack of standardization, the validity of tests can not be determined through scientific experimentation. The examiner may therefore influence the outcomes of the test due to its subjective nature.

A fundamental flaw in the polygraph test as articulated by Bell and Grubin (2010, p.54) is that “there is no psychological theory that uniquely ties physiological arousal, as measured by the polygraph, to deception”. Grubin and Bell (2010)l asserts that despite claims to the contrary, the techniques and methods used in polygraphy have changed very little since its invention in the early 1900s.

The supposed computerization of the polygraph has done little to change the theory and methodology utilized in polygraph tests. Attempts at explaining physiological detection of deception as a factor of guilt have up to this point been unsuccessful and the psychological explanations offered up to this point are unconvincing.

Research findings regarding the basic science behind polygraphy technique reveal that the theoretical rationale of the technique is at best very weak. More specifically, findings from the National Research Council demonstrate that polygraphs can not “differentiate fear, arousal, or other emotional states that are triggered in response to relevant or comparison questions” (National Research Council, 2003, p.13).

Considering the fact that the polygraph test relies primarily on these physiological reactions to ascertain truth or falsehood, the lack of ability to differentiate greatly undermines the accuracy of CQT. Furedy and Heslegrave (1991) note that part of the problem that polygraphs are subject to is in differentiating the subtle pschological processes that are produced from telling the truth of lying.

Inter-rater reliability of the polygraph test varies significantly across studies. Test-retest reliability is the “ability of a test to measure a trait that is supposed to be stable over time” (Maschke & Scalabrini, 2005). Scientific methods are characterized by high measures of retest reliability and high rates of accuracy across various independent tests.

Using a sample of mock crime studies, Kircher, Horowitz and Raskin (1988) found that the accuracy levels ranged from 65% to 100%. Bell and Grubin (2010) propose that the variance in accuracy of the polygraph test as is evident from studies is as a result of the differences in the subjects, varying levels of incentives for passing the test and the specific method of determining guilt or innocence that is used by the professional.

The accuracy of the polygraph test is further compromised by the less subtle physiological changes that result from factors that are external to truth or lies such as anger and anxiety to name but a few.

For instance, if the subject is feeling pressured to pass the test or is made anxious by the nature of questions asked, he will exhibit anxiety which will produced increased physiological activity regardless of his truthfulness or falseness in answering the questions (Furedy & Heslegrave, 1991). Since the polygraph test does not take into consideration the many other external variables that may result in physiological activity, the results will be flawed.

It is possible that the validity of polygraph testing may be increased in future following advances being made in functional magnetic resonance imaging (fMRI). Grubin and Bell (2010) state that fMRI will provide the means with which to explore and better understand the correlation of polygraph testing with psycho physiological. By so doing, a scientifically sound basis for the operation of the polygraph will be found. With this, repeatability may be assured and hence the validity of the test. Until such advances are made, the accuracy of the polygraph test remains wanting.


The appeal of a machine or technology that purports to detect deception is great and for hundreds of years, man has been searching for such a device. Bell and Grubin (2010) declare that while research on the polygraph test has been conducted since the onset of the 20th century, it is still unclear as to what extent polygraphy is a valid means for detecting deception. While proponents of CQT state that the results from the test are significantly higher than chance, the variance in accuracy acts as a major obstacle for adopting CQT as evidence in court rooms.

A survey by Iacono and Lykken (1997) revealed that “the CQT can be beaten by augmenting one’s response to the control questions”. This can have a number of negative impacts in criminal justice. To begin with, the investigating officers can be steered away from a criminal who has allegedly passed the test.

If the evidence from the test is presented to a court of law, it may lead to the acquittal of a guilty party who used false means to beat the test. In either case, the efficiency of the criminal justice system is hindered by reliance on the polygraph test. Maschke and Scalabrini (2005) ominously state that it is unsafe to assume that everyone who passes a polygraph test has told the truth.

In countries where results of a polygraphic examination are admissible evidence in courts of law, the polygrapher is viewed as an expert witness who determines whether the suspect has been truthful or deceptive (Furedy & Heslegrave, 1991). The evidence presented on the strength of the polygraph has a huge bearing on the judgment passed due to the doctrine of polygraphic infallibility. Furedy and Heslegrave (1991) reveal that the perceived guilt of an accused person in court may be heightened as a result of the presentation of polygraphic evidence before the judge and jury..

While the polygraph does present itself as a novel tool for crime fighting, the role played by the criminal justice system is imperative for the well being of the society and the fairness of the system must be unquestionable. As has been seen in this paper, the polygraph is not absolute and if it is used in the court system, the fairness of the court may be compromised.

Even so, the polygraph test is useful in assisting the investigating officer to decide on the direction that the investigation should take. Therefore, the polygraph test should be used by investigators to aid in their investigation efforts but it should be barred from the court rooms.


This paper argues that polygraph evidence should not be admissible in federal courts. To reinforce this assertion, the paper has demonstrated the inherent flaws that exist in polygraph tests. The paper has began by articulated the various assumptions that are taken in the use of the polygraph.

This paper has demonstrated that the theory underlying polygraph tests if fundamentally flawed and the accuracy and validity of these technique is varies from chance to perfection hence making polygraph tests scientifically unsound.

The paper has also noted that there are many factors that influence the accuracy of polygraph tests. From these revelations, it can be authoritatively stated that the accuracy level of polygraph tests falls below the acceptable level for the court systems. Polygraph evidence should therefore stay out of our court rooms until such a time that the validity of this technique is increased and the accuracy made absolute.


Bell, B.G., & Grubin, D. (2010). “Functional Magnetic Resonance Imaging may promote theoretical understanding of the Polygraph Test”. The Journal of Forensic Psychiatry & Psychology Vol. 21, No. 1, February 2010, 52–65

Ben-Shakhar, G. (2002). A Critical Review of The Control Question Test. San Diego, CA: Academic Press. Furedy, J.J., & Heslegrave, R. J. (1991). “The Forensic Use of the Polygraph: A Psychophysiological Analysis of Current Trends And Future Prospects”. Advances in Psychophysiology, Volume 4, pages 157-189.

Iacono, W.G., & Lykken, D.T. (1997) “The Validity of the Lie Detector: Two Surveys of Scientific Opinion,” Journal of Applied Psychology, Vol. 82 (1997), No. 3, pp. 426–33. Abstract: Kircher, J.C., Horowitz, S.W., & Raskin, D.C. (1988). “Meta-analysis of mock crime studies of the control question polygraph technique”. Law and Human Behavior, 12, 79–90.s Maschke, W.G., & Scalabrini. (2005). The Lie Behind the Lie Detector. AntiPolygraph Organization.

National Research Council. (2003). The Polygraph and Lie Detection. Committee to Review the Scientific Evidence on the Polygraph. Division of Behavioral and Social Sciences and Education. Washington, DC: The National Academies Press.

Raskin, D.C., & Honts, C.R. (2002). The Comparison Question Test. San Diego, CA: Academic Pres

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