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Lie Detector Test

The word polygraph comes form the Greek for “many writings.” The polygraph machine measures physiological information from the body: breathing, blood pressure, and perspiration. The faster the breathing, the higher the blood pressure, and the greater the amount of sweat, the more likelihood the person being tested is nervous.

Although it had been suggested in the nineteenth and early twentieth centuries that physiological changes could help determine whether a person was telling the truth, the first serious effort to apply this information came in 1920 when John Larson, a police officer in Berkeley, California, developed a device (which he called a polygraph) that could measure breathing and blood pressure. Larson believed that his invention could help determine whether a suspect was telling the truth. When the results of a polygraph test were included as evidence in a criminal case in 1923, they were challenged, and the D.C. District Circuit Court ruled in U.S. v. Frye that polygraph evidence needed to meet three criteria to be accepted:

(1) that the general scientific community must acknowledge the test’s reliability,
(2) that the person conducting the test must be qualified to do so, and
(3) that it can be proven that correct procedures were followed

Known as the “Frye test,” it remained the judicial standard for 70 years.

During that time, scientists worked at refining Larson’s invention. Leonarde Keeler, who had worked with Larson, began developing more sensitive polygraph machines in the 1930s, even starting a polygraph school in 1948.

Through the years, polygraphs were used by law enforcement agencies, but they were not considered definitive. To begin with, the person who is hooked up to the polygraph would already be quite nervous, and to have tubes placed on the chest, a blood pressure cuff on the arm, and metal plates on the fingers would not relax most people. Moreover, there is a difference of opinion on the accuracy of polygraph tests. The American Polygraph Association has stated that inconclusive polygraph results are not the same as incorrect results. Yet typically inconclusive readings are figured in with incorrect ones when establishing a percentage of accuracy.

Polygraphs (“Lie Detectors”)

Polygraph experts continued to fine-tune the machines, and also developed a questioning technique that was intended to produce fewer incorrect readings (the subject is asked to respond “yes” or “no” to questions, and unrelated questions are mixed in with relevant ones; this is meant to eliminate nervous affect).

In 1975, federal judges were given more discretion about the admissibility of evidence under new “Federal Rules of Evidence.” Thus, a judge could allow a jury to consider polygraph results even if they did not pass the Frye Test. In 1993, the U.S. Supreme Court issued an opinion on Daubert v. Merrell Dow Phramaceuticals that definitively replaced the Frye standard. The court said that judges could admit certain scientific evidence as long as the theory behind it could be been tested, it had been subject to peer review and publication, the potential error was known, and the scientific community in general accepted the theory. In the 1998 case of U.S. v. Scheffer, the U.S. Supreme Court ruled that polygraph tests did not have to be admitted as evidence in military trials. (President George H.W. Bush had banned the admission of polygraph evidence from military trials in 1991, citing their unreliability.) But it did not ban polygraph evidence outright. Daubert grants judges the right to determine whether polygraph evidence can be used or ignored, so it is generally up to the judge.

The polygraph has also been used to pre-screen job applicants or to test employees to measure their truthfulness about such issues as drug use or theft. In 1988 Congress passed the Employee Polygraph Protection Act (EPPA), which prohibited business from using polygraph evidence to pre-screen employees or to test current employees, and which prohibited companies from disciplining or firing employees solely for failing a polygraph test. (Polygraphs can be used if an employer can show other evidence against an employee, but the employee still has the right to refuse.) EPPA does not apply to government workers.

Lie Detector Tests: Do They Tell the Truth?

Learn how polygraph tests work, as well as what supporters and detractors have to say about them.

The theory underlying a lie detector test — or a polygraph test, in more scientific terms — is that lying is stressful, and that this stress can be measured and recorded on a polygraph machine. Lie detectors are called polygraphs because the test consists of simultaneously monitoring several of the suspect’s physiological functions — breathing, pulse, and galvanic skin response — and printing out the results on graph paper.

The printout shows exactly when, during the questioning period, the biologic responses occurred. If the period of greatest biologic reaction lines up with the key questions on the graph paper — the questions that would implicate the person as being involved with the crime — stress is presumed. And along with this presumption of stress comes a second presumption: that the stress indicates a lie.

Arguments For and Against

Supporters of lie detector tests claim that the test is reliable because:

• very few people can control all three physiological functions at the same time, and
• polygraph examiners run preexamination tests on the suspect that enable the examiners to measure that individual’s reaction to telling a lie.

On the other hand, critics of polygraph testing argue that:

• many subjects can indeed conceal stress even when they are aware that they are lying, and
• there is no reliable way to distinguish an individual’s stress generated by the test and the stress generated by a particular lie.

The courts in most jurisdictions doubt the reliability of lie detector tests and refuse to admit the results into evidence. Some states do admit the results of polygraph tests at trial if the prosecution and defendant agree prior to the test that its results will be admissible.

Are Lie Detectors Telling the Truth?

You may wonder how, in the absence of a confession, a polygraph operator can confidently determine whether a person is lying. Don’t most people — even innocent ones — get stressed when being asked questions that might land them in big trouble? Yes, but the polygraph operator has techniques to overcome this problem. Before getting to the nitty-gritty of the issue (“Did you do it? Were you There? Do you have any personal knowledge of what happened?”) the operator first asks a series of questions, some of which are emotionally neutral and some of which are calculated to cause emotional discomfort based on the test subject’s personal circumstances. The subject’s physiological responses to these questions are meticulously calibrated. Then, when the operator gets around to the core questions, the responses to those questions can be measured and compared to the responses produced by the neutral and control questions. It’s true, a lot of devils can live in the space of relative anxiety measurements, but numerous independent tests have indicated an accuracy rate in the 80-90% range.

Lie Detector Tests: Do They Tell the Truth?

So if these tests are so accurate, why aren’t they required in every situation where truth is at issue? Why spend billions of dollars on jury trials and independent prosecutors when we could just “wire up” the key witnesses and get at the truth with no fuss and no muss?

Some people are so divorced from morality or a guilty conscience that they may test honest — because they are really good liars or have convinced themselves of a truth that isn’t the truth at all. It may also be possible to throw the results through other methods, such as yogic or biofeedback training, the “nail in the shoe” trick (putting a sharp nail in your shoe to cause yourself pain during the questions to skew the polygraph results), or using a legal or illegal drug to calibrate one’s emotions. Simply put, there is no way to turn a lie detector test into a slam dunk. For this reason, most courts will not admit polygraph results unless both sides to the case agree.

If you have any questions about lie detector test contact San Diego Criminal Attorney Vik Monder at 619.405.0063 or visit San Diego Criminal Defense