About Lie Detectors
The polygraph, popularly known as the lie detector, is a poorly understood device. Often the stuff of crime dramas, polygraph results are actually inadmissible in court in most states. More often they are used in security checks on personnel, but they are not especially reliable even in that role.
How Does It Work?
A polygraph works by monitoring a subject's physiological responses under questioning, with the premise being that false responses will cause an observable, involuntary change in behavior. Polygraphs monitor blood pressure, pulse rate, respiration rhythm and temperature.
Warning: Reliability
There is little scientific evidence proving that the technique actually works. Critics describe the polygraph as little more than a dramatic interrogation prop, which will make a nervous and guilty person even more nervous. Interpreting the results of a polygraph are more subjective than objective, and USA Today reported a 1997 study of more than 400 psychologists that indicated little faith in the polygraph. In 2003, the National Academy of Sciences (NAS) reported that the polygraph was "unreliable, unscientific and biased." Infamous spies like Aldrich Aimes and Ana Belen Montes both passed polygraph exams.
Cheating the Test
Cheating a lie detector is actually easy for a disciplined person with a good grip on her emotions. The standard technique is to stay calm and keep the pulse rate under control during "live questions," but to think of something scary or horrible, or to prick themselves with a sharp pin, to elevate the pulse for "control questions" (blank questions meant to establish a base response). A person can even train in this method with little more than a pulse monitor. When CIA turncoat Aldrich Aimes asked his KGB handler what to do about the polygraph, he was advised to show up well rested, stay calm and to get friendly with the lie detector examiner.
Polygraphs in Court
Polygraph evidence is admissible in court in only 19 states, and is only admitted with limitations. The only state to admit polygraph records in court is New Mexico, with the others allowing the examiner to testify. At the Federal level, admitting polygraph evidence is subject to the decision of the judge in question. Despite this decidedly mixed attitude on the part of the courts, lie detectors are still used by law enforcement, and both state and local prosecutors. However, no one can be forced to undergo a lie detector test.
Screenings
Given that lie detector tests are viewed dubiously by the courts, their major use is in security checks on personnel. In the private sector, the Employee Polygraph Protection Act of 1988 prohibits taking a lie detector exam as a condition for employment, and also as a general condition for continued employment. However, it is permissible under Federal law in some circumstances. Five states have laws on the books making it illegal for any employer to order the use of a polygraph, or punish an employee for not taking one. The US military and the intelligence services use polygraphs as part of their security screening, requiring an exam to get a security clearance, and then periodic exams to keep one.
