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Accuracy of the Polygraph Examination


Lie detector tests have become a popular cultural icon – from crime dramas to comedies to advertisements – the picture of a polygraph pen wildly gyrating on a moving chart is readily recognized symbol.

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The instrument typically used to conduct polygraph tests consists of a physiological recorder that assesses three indicators of autonomic arousal: heart rate/blood pressure, respiration, and skin conductivity. Most examiners today use computerized recording systems. Rate and depth of respiration are measured by pneumographs wrapped around a subject’s chest. Cardiovascular activity is assessed by a blood pressure cuff. Skin conductivity (called the galvanic skin or electrodermal response) is measured through electrodes attached to a subject’s fingertips.

The recording instrument and questioning techniques are only used during a part of the polygraph examination. A typical examination includes a pre-test phase during which the technique is explained and each test question reviewed. The pre-test interview is designed to ensure that subjects understand the questions and to induce a subject’s concern about being deceptive.

Polygraph examinations often include a procedure called a “stimulation test,” which is a demonstration of the instrument’s accuracy in detecting deception.

According to wikapedia (https://en.wikipedia.org/wiki/Polygraph#Validity) and NAS studies done in 2003, the National Academy of Sciences (NAS) issued a report entitled “The Polygraph and Lie Detection”. The NAS found that the majority of polygraph research was “unreliable, unscientific and biased”, concluding that 57 of the approximately 80 research studies that the APA relies on to come to their conclusions were significantly flawed. These studies did show that specific-incident polygraph testing, in a person untrained in counter-measures, could discern the truth at “a level greater than chance, yet short of perfection”. However, due to several flaws, the levels of accuracy shown in these studies “are almost certainly higher than actual polygraph accuracy of specific-incident testing in the field”.

When polygraphs are used as a screening tool the level of accuracy drops to such a level that the NAS extrapolated that if the test were sensitive enough to detect 80% of spies, this would hardly be sufficient anyway. Let us take for example a hypothetical polygraph screening of a body of 10,000 employees among which are 10 spies. With an 80% success rate, the polygraph test would show that 8 spies and 1,992 non-spies fail the test. Thus, roughly 99.6 percent of positives (those failing the test) would be false positives. The NAS concluded that the polygraph “…may have some utility” but that there is “little basis for the expectation that a polygraph test could have extremely high accuracy.”

Even the term “lie detector,” used to refer to polygraph testing, is a misnomer. So-called “lie detection” involves inferring deception through analysis of physiological responses to a structured,  series of questions. Precom Polygraph Examiners are fully trained in Forensic Assessment Interviewing Techniques (FAINT). Our examiners will add the FAINT to the polygraph pre-test in order to maximize the result and outcome of such test.

At the API we utilize the most accurate question formation techniques in order to up the % of accuracy and eliminate the possible “false positives and false negatives. Studies done on the IZCT question technique showed this technique to be 96% accurate. Therefore, in short, there is no fail proof deception detection method currently.


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