Polygraph—more commonly called lie detector—tests are not often used in divorce or criminal cases. In a criminal case a polygraph can be used to determine key facts in a case whereas in a divorce the polygraph may be used to determine certain habits of one or both spouses. The underlying premise with a polygraph test is that lying is stressful and that stress can be measured may be accurate, there are a number of factors that make polygraph tests unreliable.
A lie detector is more accurately called a polygraph because it measures multiple (thus “poly-“) physiological functions, including breathing, pulse, and galvanic skin reactions, and prints the results out on graph paper for a specialist to read. The printout demonstrates precisely when during an interview the biologic responses happen, and the theory is that the greatest reactions indicated would suggest the greatest amount of stress, presumably that stress is related to the subject lying or becoming nervous when answering a particular question. The nature of this test does present some legal issues when attempting to enter its results into evidence.
Those in favor of using polygraph tests argue that:
• A very small percentage of the population can control all 3 physiological reactions at the same time, and
• Polygraph experts run pre-examination assessments on subjects in order to gauge when the suspect is telling a lie.
• Those opposing the use of lie detectors contend that:
• Many individuals can conceal indicators of stress, even when they are in fact lying, and
• There is no dependable way to determine whether the measured stress is created by the testing situation itself or by an actual lie.
Since most people will become nervous during questioning, polygraph technicians first calibrate their instrument before the interview begins. During this calibration period, the technician will ask a series of questions—some emotionally-neutral and others emotionally-charged—in order to meticulously measure the physiological responses of the subject. This pre-examination assessment allows the expert to then compare the results of the calibration questions to the subject’s responses during the core interview.
Independent research has shown polygraph test results to be accurate 80 to 90 percent of the time.
Polygraphs are not 100 percent reliable. Individuals exist who are without morality or conscience; these subjects can sometimes detach themselves from reality or they can convince themselves that what they are saying—though it is a lie—is truthful, thus “passing” the polygraph.
It is also possible to train one’s bodily responses through yoga and biofeedback, as well as to regulate one’s emotional responses through the use of legal or illegal substances.
Since polygraph testing is not considered reliable every time, lie detector tests are generally not considered admissible as evidence in a court of law unless both the prosecution and the defense agree upon it before the testing begins.
Guest author Mario Madrid has been practicing criminal law for over five years. He recently opened up his own criminal law firm, Madrid Law. Mario defends a variety of white collar crimes including identity theft, wire fraud, embezzlement and more.