Polygraphs ("Lie Detectors")
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.
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