Written Test Could Improve Polygraph Accuracy

A written test used in conjunction with a polygraph examination could increase the chances of obtaining accurate results concludes a new study published in Psychophysiology. The test, called Symptom Validity Testing, which has already been used to detect amnesia and post traumatic stress disorder, greatly increases the chance of obtaining accurate results according to researchers.

Polygraph testing is calibrated to avoid any false positives, causing polygraph readers to be very conservative in detecting lies. While this system protects against innocent people being wrongly accused of lying, a skilled liar can usually fool the test.

Polygraphs work by measuring changes in physiological responses during questioning such as pulse, respiration, and blood pressure. The results are carefully read by a trained professional to determine whether or not the person taking the test is lying.

Symptom Validity Testing looks at a completely separate set of responses to gauge whether or not a suspect is lying. Innocent people, when asked about crimes can generate a random pattern of results during the test. Guilty people, on the other hand, have difficulty generating a random pattern, indicating that they might be lying.

This test ideally should be combined with the concealed information polygraph test to achieve the best outcome. The concealed information polygraph test is an already developed technique, but is not as popular as other testing methods.

"We showed that the accuracy of a Concealed Information Test can be increased by adding a simple pencil and paper test," says lead author Ewout Meijer of Maastricht University. "When 'guilty' participants were forced to choose one answer for each question, a substantial proportion did not succeed in producing the random pattern that can be expected from 'innocent' participants."

Not only is Symptom Validity Testing an easy way to increase the effectiveness of the polygraph examinations, but it is also an inexpensive paper and pencil test. During research into the method, the tests correctly determined if a person was faking amnesia as well as when a suspect was lying.

If more accurate results can be achieved by using the combined results, it may improve the chances that polygraph results could be admitted in court proceedings. Currently in the United States, no one can be forced to take a lie detector test and the results of a polygraph are not always admissible into evidence. Other countries have also rejected the use of the device, sighting its unreliability.
Source:

Blackwell Publishing Ltd., "Simple Test Improves Accuracy of Polygraph Results" Eurekalert