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National Academy of Sciences Report
Feb 23rd, 2003 at 5:21am
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Date: Oct. 8, 2002
Contacts: Vanee Vines, Media Relations Officer
Andrea Durham, Media Relations Assistant
(202) 334-2138; e-mail <>


Polygraph Testing Too Flawed for Security Screening

WASHINGTON The federal government should not rely on polygraph examinations for screening prospective or current employees to identify spies or other national-security risks because the test results are too inaccurate when used this way, says a new report from the National Academies' National Research Council.

Much of the evidence assessing the validity of polygraphs, also called "lie detectors," is based on their use in the investigation of specific, known events such as crimes. In these cases, lie-detector tests can differentiate lying from telling the truth at rates well above chance, but they are far from perfect. The report concludes that the polygraph's accuracy is not good enough for security screening for two reasons. First, accuracy is almost certainly lower when the tests are used this way rather than in the investigation of specific incidents. Second, the large groups of people being checked include only a tiny percentage of individuals who are guilty of the targeted offenses; tests that are sensitive enough to spot most violators will also mistakenly mark large numbers of innocent test takers as guilty. Tests that produce few of these types of errors, such as those currently used by several federal agencies, will not catch most major security violators and still will incorrectly flag truthful people as deceptive.

"National security is too important to be left to such a blunt instrument," said Stephen E. Fienberg, chair of the committee that wrote the report, and professor of statistics and computer science, Carnegie Mellon University, Pittsburgh. "The polygraph's serious limitations in employee security screening underscore the need to look more broadly for effective, alternative methods."

Concerned about potential security violations at national energy laboratories, the U.S. Department of Energy asked the Research Council to conduct a study of the scientific validity and reliability of using polygraph testing to identify personnel who may jeopardize national security. Employees who work in sensitive positions at DOE labs and similar federal sites are subject to testing by law. When used this way, however, the drawbacks of current polygraph exams are abundantly clear, the report says.

The exams include a pre-test interview between the examiner and test taker, followed by interrogation coupled with the use of a device that records an individual's physiological responses, such as respiration rate and changes in blood flow, to a series of questions. Examiners later analyze the record of these responses to help make inferences about whether someone is being honest.

Polygraph testing now rests on weak scientific underpinnings despite nearly a century of study, the committee said. And much of the available evidence for judging its validity lacks scientific rigor.

Moreover, because the largest part of the evidence comes from studies that assess lie detection related to specific events, it has limited relevance to pre- and post-employment screening, the report says. Examiners ask generic questions during security screening because they do not know what violations test takers may be concealing. Individuals may react differently to generic questions than to specific ones typically used in investigations of known events. Additionally, both examiners and test takers may have difficulty knowing whether answers to generic questions are truthful unless there are clear and consistent standards that define what type of response is justified.

Using these tests in pre-employment screening is even more complicated because examiners make inferences about individuals' future behavior based on information about previous deeds, which may differ widely from the offenses authorities hope to prevent. The committee concluded that polygraph testing is less accurate for employee screening than for investigating specific incidents.

On a more basic level, theories about how deception is linked to the physiological responses being measured have not been verified, the report says. A variety of mental and physical factors, such as anxiety about being tested, can affect polygraph results making the technique susceptible to error. Also, people can learn ways to mimic some physiological responses of truthful test takers. This is a particular concern when dealing with deceptive individuals who have strong incentives and sufficient resources to perfect certain "countermeasures" or ploys to appear honest and avoid detection. Available research sheds little light on how well examiners can systematically expose such people.

Despite its weak science base, polygraph testing is commonly believed to be a highly valid procedure for detecting lies. Popular culture and the mass media often portray lie detectors as magical mind-reading machines. The mystique surrounding the exams instead of a solid scientific foundation may account for much of their usefulness to authorities, the committee noted. Examiners' field reports and indirect scientific evidence indicate that testing programs may deter potential security violators or elicit confessions from some offenders who, unaware of the tests' weaknesses, believe that a lie detector would surely catch them.

The federal government relies heavily on polygraph testing to identify people who have committed or might commit espionage and sabotage. However, overconfidence in this method may endanger national security objectives by creating a false sense of security among lawmakers, federal employees in sensitive jobs, and the general public, the report warns. As a result, other ways to ensure safety could be neglected, creating situations that might increase the risk of security lapses. Resources could be wasted by devoting too much attention to employee screening and too little to other security measures. Plus, retention of highly skilled and valuable government workers could suffer because employees might fear the consequences of being falsely identified as dishonest.

Some potential alternatives to polygraphs show promise, but none has led to scientific breakthroughs in lie detection, the report says. Moreover, the federal government has not seriously developed the science base of any method to detect deception through the analysis of individuals' psychological and physiological reactions.

The committee called for a broad research program that would provide federal agencies with the most scientifically sound methods for deterring and detecting major security risks, and work to make government authorities fully aware of the strengths and drawbacks of their security techniques. This effort would support a variety of activities from basic research on psychological, physiological, social, and political processes related to discouraging and uncovering security threats, to studies on ways to carry out well-founded screening techniques in everyday practice. No single research approach is clearly superior.

An impartial organization that is not responsible for any aspect of detecting deception should run a considerable part of the program, the report says. Additionally, the program should follow established standards for scientific research and, without jeopardizing national security, operate under normal rules of scientific freedom and openness to the fullest possible extent.

The study was sponsored by the U.S. Department of Energy. The Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science advice under a congressional charter. A committee roster follows.

Read the full text of The Polygraph and Lie Detection for free on the Web, as well as more than 1,800 other publications from the National Academies. Printed Copies are available for purchase from the National Academy Press Web site or by calling (202) 334-3313 or 1-800-624-6242. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).

Division of Behavioral and Social Sciences and Education
Board on Behavioral, Cognitive, and Sensory Sciences
and Committee on National Statistics

Committee to Review the Scientific Evidence on the Polygraph

See referenced link for complete listing of Committee Members.

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