An instrument that simultaneously records changes in such physiological processes as heartbeat, blood pressure, and respiration, used as a lie detector by police departments, the FBI, the CIA, the KGB, the KKK, federal and state governments, and numerous private employers.
Is there any evidence that the polygraph is really able to detect lies? Well, the machine measures changes in blood pressure, breath rate and respiration rate. When a person lies it is assumed that these physiological changes occur in such a way that a trained expert can detect whether or not the person is lying. Is there a scientific formula or law which establishes a regular correlation between such physiological changes and lying? No. Is there any scientific evidence that polygraph experts can detect lies using their machine at a significantly better rate than non-experts using other methods? No. There are no machines and no experts which can detect with high degrees of accuracy when people are lying.
Some people, such as Senator Oren Hatch, don't trust the polygraph machine, even if used by an expert like Paul Minor who trained FBI agents in their use. Anita Hill passed a polygraph test administered by Minor who declared she was telling the truth about Clarence Thomas. Hatch declared that someone with a delusional disorder could pass the test if the liar really thought she was telling the truth! Pretty clever argument, but the ability of sociopaths and the deluded to pass a polygraph test is not the reason such machines cannot accurately detect lies with any accuracy greater than ordinary methods of lie detection.
The reason the polygraph is not a lie detector is because what it measures--changes in heartbeat, blood pressure, and respiration--can be caused by many things. Nervousness, anger, sadness, embarrassment and fear can all be causal factors in altering one's heart rate, blood pressure or respiration rate. Having to go to the bathroom can also be causative. There are also a number of medical conditions such as colds, headaches, constipation, or neurological and muscular problems which can cause the physiological changes measured by the polygraph. The claim that an expert can tell when the changes are due to a lie and when they are due to other factors has never been proven.
In California and, I suppose, in most other states, the results of polygraph tests are inadmissible as evidence in a court of law. This may because they are known to be unreliable, or it may be because what little benefit may be derived from using the polygraph is far outweighed by the potential for significant abuse by the police. The test can easily be used to invade a person's privacy or to issue a high-tech browbeating of suspects. Skeptics consider evidence from polygraphs no more reliable than testimony evoked under hypnosis, which is also not allowed in a court of law in California and many other states.
The American Civil Liberties Union strongly supported the passage of the Employee Polygraph Protection Act of 1988 (EPPA) which outlaws the use of the polygraph "for the purpose of rendering a diagnostic opinion regarding the honesty or dishonesty of an individual." Well, it doesn't really outlaw it across the board. Federal, state and local governments can still use the polygraph. The federal government can give polygraph tests to government contractors involved in national security projects. In the private sector, security and pharmaceutical firms can still use the polygraph on current or prospective employees. Actually, any employer can administer polygraph tests under certain circumstances:
Any employer may administer "lie detector" tests in connection with an ongoing investigation of an economic loss or injury to his/her business on these conditions: The employee under suspicion must have had access to the property, and the employer must state in writing the basis for a reasonable suspicion that the employee was guilty. ACLU
The ACLU supported the EPPA not only because of the lack of evidence for the accuracy of the polygraph, but because of abuses related with its administration, including, but not limited to, the invasion of privacy.
For example, in order to establish "normal" physiological reactions of the person being tested, "lie detector" examiners ask questions that purposely embarrass, frighten and humiliate workers. An ACLU lawsuit in l987 revealed that state employees in North Carolina were routinely asked to answer such questions as "When was the last time you unintentionally exposed yourself after drinking?" and "Who was the last child that got you sexy?" Polygraphs have been used by unscrupulous employers to harass union organizers and whistle-blowers, to coerce employees into "confessing" infractions they did not commit, and to falsely implicate fellow employees. ACLU
Why would so many government and law enforcement agencies, and so many private sector employers, want to use the polygraph if there is no scientific proof of their validity? Is it just wishful thinking? They want to believe there is a quick and dirty test to determine who's lying and who's not, so they blind themselves to the lack of evidence? That's probably a large part of it, but I don't think it explains everything. I think that other factors are involved. One factor is the esoteric technology factor. The machine looks like a sophisticated, space- age device of modern technology. It can be administered correctly only by experts trained in its arcane ways. Non-experts are at the mercy of the high-tech, specially trained wizards who alone can deliver the prize: a decision as to who is lying and who is not.
Another factor is the pragmatic fallacy factor: it works! Case after case can be used to exemplify that the polygraph works. There are the cases of those who failed the test and whose lying was corroborated by other evidence. There are the cases of those who, seeing they are failing the test, suddenly confess. What is the evidence that the rate of correct identification of lying corroborated by extrinsic evidence is greater than the rate of identification of lying by non-technological means? There isn't any. The proofs are anecdotal or based on fallacious reasoning such as thinking that a correlation proves a causal connection.
It is possible that one of the main reasons so many government, law enforcement and private sector employers want to use polygraphs is because they think the test will frighten away liars and cheats who are seeking jobs, or it will frighten those accused of wrongdoing into confessing or telling on others. In other words, the users of the machine don't really believe it can detect lies, but they know that the people they administer it to think the machine can catch them in a lie. So, the result is same as if the test really worked: they don't hire the liar/cheat or they catch the dishonest employee.
What is true of the polygraph is true of all other "honesty" or "integrity" tests. There is no evidence supporting the validity of the claim that such tests can accurately measure truth, lying, honesty or the tendency of intelligent people to deceive themselves.
reader comments
28 Oct 1996
I thought this treatment of polygraph machines as "lie detectors" was
pretty good. Let's face it: this is Gilligan's Island science, not real
science.
You left out one interesting issue, though. How come Phil Klass, considered (by "skeptics") as "the leading UFO skeptic," puts such a pathetic credence in the things? If someone makes a claim Klass doesn't like, he wants the guy to take a "lie detector" test. Why don't the other "skeptics" wise up their colleague so he'll stop making such a fool of himself--and proving, by the way, to those who want to believe it, that the "skeptics" have no real arguments for their position? Or does he just keep doing it because he wants to cow people into submission, and not say they've had experiences he "knows" they couldn't?
Dan Clore
reply: I agree with you. Lie detector tests would not be of much value in testing alleged ufo sitings or alien abductions. I suppose the threat of such a test might scare some fabricators into owning up, but other than that I think such tests are of little interest.
further reading
"Lie Detector Testing," ACLU paper
Beyerstein, Dale. "The Poor Man's Polygraph," in Rational Enquirer, Vol 3, No. 1, Jul 89.
Davis, R. C., "Physiological Responses as a Means of Evaluating Information," in A. D. Biderman & H. Zimmer, eds., The Manipulation of Human Behavior (Wiley, 1961).
Lykken, David Thoreson. A Tremor in the Blood : Uses and Abuses of the Lie Detector (New York : McGraw-Hill, 1981).
Jussim, Daniel. "Ouija Board Justice" in Florida : the Polygraph Comes to School, in Civil Liberties, No. 358 (summer-fall 1986)
Morris, Roberta, "The Admissibility of Evidence Derived from Hypnosis and Polygraphy," in Psychological Methods in Criminal Investigation and Evidence, ed. by David Raskin (Springer Publishing Co., 1989.)
Raskin, David, "Polygraph Techniques for the Detection of Deception," in Psychological Methods in Criminal Investigation and Evidence, ed. by David Raskin (Springer Publishing Co.,1989.)
Shneour, Elie. "Lying about polygraph tests," Skeptical Inquirer Spring 1990 (vol.14, no.3).
"Polygraph tests are degrading, don't work-- and should be banned," in Civil Liberties, No. 355 (fall 1985).