views updated May 29 2018


An instrument used to measure physiological responses in humans when they are questioned in order to determine if their answers are truthful.

Also known as a "lie detector," the polygraph has a controversial history in U.S. law. First developed in the late nineteenth century, its modern incarnation is an electromechanical device that is attached to a subject's body during an interview. The discipline of polygraphy is based on the theory that by recording involuntary physiological changes in the subject, the polygraph yields data that can be interpreted to determine whether the subject is telling the truth. Supporters of the scientific validity of the polygraph claim that results are approximately 90 percent accurate. For much of the twentieth century, however, polygraph evidence was inadmissible in criminal cases on grounds of unreliability. Polygraph evidence was admissible in civil cases, however, and it was also used widely in law enforcement, government, and industry.

Polygraphy uses a variety of formats. Until the 1950s the format was the relevant/irrelevant (R/I) test; it rested on the now discredited belief that a subject produces a specific identifiable physiological response when lying. The R/I test has been replaced by the control question (CQ) format, the only format routinely used in forensic tests. Typically, a trained examiner fits a subject with sensors to measure respiration, heart rate and blood pressure, and perspiration, which the polygraph records using pens on graph paper. The examiner asks a series of questions, including control questions that are designed to provoke anxiety and denial. Later, another examiner compares these answers with answers pertaining to the matter at hand. This is known as numerical CQ testing. So-called global CQ testing includes a more subjective component: one examiner scores the test while also factoring in the subject's observable physical responses, such as movement, expression, and voice.

In U.S. courts, the use of the polygraph was first addressed in 1923. In refusing to admit polygraph evidence in a murder case, the Court of Appeals for the District of Columbia created a legal standard that would last for nearly 70 years (Frye v. United States, 54 App. D.C. 46, 293 F. 1013 [1923]). This standard came to be known as the Frye rule, or general acceptance test. To be admissible in court, novel scientific evidence first must have gained general acceptance in its scientific field.

The Frye rule applied broadly to all scientific evidence, including polygraph evidence. Other appellate courts followed the court's standard throughout most of the century, primarily because polygraphy never gained widespread acceptance among scientists. Nonetheless, polygraph evidence was used in civil lawsuits, and police agencies, businesses, and government offices continued to use the polygraph regularly to provide evidence, screen job applicants, and investigate security risks.

Advances in polygraphy helped spur a judicial reevaluation, but more important was the adoption of the federal rules of evidence in the 1970s. Rule 702 set an important new standard for the admission of scientific evidence:

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.

Over the next two decades, appellate courts authorized use of polygraph evidence in a few state courts, a trend followed by the U.S. Court of Appeals for the Eleventh Circuit and the military courts. Then, in 1993, in a case not specifically related to the polygraph, the U.S. Supreme Court held that Rule 702 replaced the Frye test (Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469). In essence, the Court said that the standard of general scientific acceptance was not as important as whether expert testimony can assist jurors. Soon thereafter, several federal courts reconsidered their long-standing ban on polygraph evidence and determined that they now had the discretion to permit its introduction at trial.

Congress also reexamined the use of the polygraph in industry. In 1988, lawmakers responded to civil liberty concerns about the abuse of polygraph testing in private industry by passing the Employee Polygraph Protection Act (29 U.S.C.A. §§ 2001 et seq.). The law bars preemployment testing in banking, retail, and other private industries and also makes it illegal for employers to fire, discriminate against, or discipline employees who refuse to submit to polygraph tests. The act exempts government employers, private industry when an employee is under investigation for economic injury suffered by the employer, and all security services and industries that manufacture, distribute, or dispense controlled substances.

In military trials, the situation was different. In United States v. Scheffer, 523 U.S. 303, 118 S. Ct. 1261, 140 L. Ed. 2d 413 (1998), the Supreme Court addressed the claim of airman Edward G. Scheffer that prohibiting the introduction of polygraph evidence during his court-martial (military criminal trial) violated his constitutional rights. Under Military Rule of Evidence 707, polygraph evidence is not allowed in court-martial proceedings. So, although Scheffer, who was accused of, among other things, taking illegal drugs, passed a polygraph, it was inadmissible as evidence. A federal court of appeals reversed the court-martial, stating that excluding the polygraph evidence did, in fact, violate Scheffer's right to present a defense as guaranteed by the sixth amendment. Upon review, the Supreme Court upheld Military Rule of Evidence 707. In the opinion of the Court, "State and federal governments unquestionably have a legitimate interest in ensuring that reliable evidence is presented to the trier of fact in a criminal trial." However, "there is simply no consensus that polygraph evidence is reliable."

further readings

Arendell, Robert L., and Stephen C. Peters. 1996. "Revisiting the Admissibility of Polygraph Evidence After Daubert." Colorado Lawyer 25 (February).

McCall, James R. 1996. "Misconceptions and Reevaluation—Polygraph Admissibility After Rock and Daubert." University of Illinois Law Review.

Segrave, Kerry. 2004. Lie Detectors: A Social History. Jefferson, N.C.: McFarland.

Sleek, Scott. 1998. "Psychologists Debate Merits of the Polygraph." APA Monitor (June).


views updated May 14 2018


The polygraph or so-called lie detector measures physiological responses to stress experienced by a subject during the course of an interrogation. The instrument monitors three physiological states: (a) cardio-vascular responses manifested by changes in blood pressure and pulse rate; (b) galvanic skin resistance that lowers as perspiration increases; and (c) breathing patterns that respond to changes in tension. Changes in any of these patterns can be detected as the subject experiences emotional reactions. The theory behind the polygraph assumes that people encounter measurable physiological changes in the act of deception. The heartbeat increases, blood pressure goes up, breathing rhythms change, and perspiration increases. All of these reactions are recorded on a moving chart for analysis by a trained polygraph technician.

The physiological connection with deception was assumed in the eighteenth century. English novelist Daniel Defoe suggested that "Guilt always carries fear around with it, there is a tremor in the blood of a thief, that, if attended to, would effectually discover him" (Gale 1988, p. 158). In 1915 Harvard psychologist William Marston devised an instrument to monitor the blood pressure of a subject under interrogation. In 1921 medical student John Larson came up with the first true polygraph, adding a measure of respiration along with blood pressure. In the 1930s, Leonarde Keeler integrated Larson's instrument with measurement of electrical skin conductivity into a single machine (Block 1977). Keeler's instrument remains in controversial use in the early twenty-first century in forensic and employment practice.

Supporters of the polygraph claim that it "is one of the most accurate means available to determine truth and deception" (American Polygraph Association 2002, Internet site). But polygraph credibility has yet to become accepted by the scientific community. A major study by the National Academy of Sciences (NAS) in 2002 found that while polygraph data is reliable, it lacks validity. Reliability is a measure of consistency, suggesting that the results are the same across different times, places, subjects, and conditions. Validity is a measure of appropriateness, suggesting that the test actually measures what it purports to measure. The NAS study found that if there were ten spies among 10,000 government employees, the lie detector would catch eight of them, but 1,598 loyal staff workers would also be falsely accused of deception. If the polygraph tests were adjusted to a much lower sensitivity, only forty-one people would be wrongly accused, but eight of the ten spies would escape detection (Moore et. al 2002). In other words, the polygraph is highly prone to type ii errors or false positives.

Because of such problems, use of the polygraph is practiced only at the fringes of legal and forensic practice, but it is in active use. The polygraph is utilized more for its utilitarian value to extract information than for its ability to measure truth or lies (Lykken 1984). Armed with a deceptively scientific instrument, an investigator may be perceived as able to read the mind of a subject. The ethical use of lie detection has been rationalized for its ability to extract information, even though the instrument cannot accurately discriminate between truth and lies. In this sense, Immanuel Kant's categorical imperative yields to John Stuart Mill's utilitarian ethic. The end of truth justifies for the modern detective the means of lying. Technical deception is practiced as a means of extracting reluctant truths.


SEE ALSO Biometrics;Crime;Justice;Police.


Block, Eugene G. (1977). Lie Detectors: Their History and Use. New York: David McKay.

Gale, Anthony, ed. (1988). The Polygraph Test—Lies, Truth and Science. London: Sage.

Lykken, David Thoreson. (1984). "Polygraphic Interrogation." Nature 307: 681–684. Professor of psychology at the University of Minnesota and past president of the Society for Psychophysiological Research, David Lykken has been a leading critic of polygraph industry-sponsored research studies that claim high levels of accuracy.

Marston, William. (1924). "A Theory of Emotions and Affection Based upon Systolic Blood Pressure Studies." American Journal of Psychology 35: 469–506.

Moore, Mark H.; Carol V. Petrie; and Anthony A. Braga, eds. (2002). The Polygraph and Lie Detection..Washington, DC: National Academy Press. This publication from the National Academy of Sciences is a report of the Committee to Review the Scientific Evidence on the Polygraph, chaired by Stephen E. Fienberg, professor of statistics at Carnegie Mellon University. The committee's charge was to review research on polygraph examinations with specific focus on the reliability and validity of polygraph test results.


American Polygraph Association. "What is a Polygraph?" Available from http://www.polygraphplace.com/docs/information.shtml#polygraph. The American Polygraph Association represents the position and the interests of the polygraph industry.


views updated May 29 2018

pol·y·graph / ˈpäliˌgraf/ • n. a machine designed to detect and record changes in physiological characteristics, such as a person's pulse and breathing rates, used esp. as a lie detector. ∎  a lie-detector test carried out with a machine of this type.DERIVATIVES: pol·y·graph·ic / ˌpäliˈgrafik/ adj.


views updated May 09 2018

polygraph See lie detector