The truth about the polygraph

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The Polygraph Test has become both famous and infamous through the popularity of its presence in crime dramas, dramatised on TV and in movies. The result of this increased attention and exposure is that there seems to be a rise of scepticism about the validity and value of taking or administering a polygraph test.

It is also apparent that there are many misconceptions about the polygraph or so called ‘lie detector’ test. Many of these misconceptions can lead to faulty or misinterpreted results. However, if the test is administered by highly trained and qualified professionals it does offer some valuable information.

According to the American Psychological Association: “The Polygraph involves inferring deception through analysis of physiological responses to a structured, but unstandardised, series of questions.”

The Association goes on to confirm that the polygraph test does not ‘detect lies’ as such, but rather monitors physiological behaviours in the body that could indicate that a person has reason to be anxious and/or calm upon answering a certain question. That information thus highlights where problem areas are, or rather, areas that perhaps need further investigation.

The physiological changes that are being monitored are three indicators of autonomic arousal. The first is respiration, measured by monitoring the rate and depth as recorded by pneumographs, which are wrapped around the chest. The second is heart rate and/or activity, measured using a blood pressure cuff. The third is skin conductivity, measured through electrodes attached to the fingertips. This measures the galvanic skin or electrodermal response.

The phases of the polygraph test include the Pre-Test Phase, the Simulation Test Phase, the Testing Phase and the Analysis Phase. In the Pre-Test Phase the technicality of the test is talked through and each question is reviewed. The person being tested has a chance to make sure that they understand what the questions mean so as to alleviate panic at a question during the Testing Phase. “It is imperative that the technicians conducting the test are highly trained and skilled. This is not merely a computer telling you if someone is lying or not. It is a very intricate process of assessment that requires the utmost professionalism and attention to detail,” explains Jacki Condon, Managing Director of Apache Security Services.

During the Simulation Test Phase, subjects are questioned with known truths and lies so as to get their individual physiological readings in a ‘truthful’ versus ‘deceptive’ state. In the Testing Phase, target and control questions are asked and physiological responses are recorded. During the final Analysis Phase, the results are analysed, and indicators of possible deception and/or areas of interest are marked for further investigation.



“The polygraph test is a highly complex system that, when used correctly, can be incredibly valuable when trying to ascertain areas of concern or interest. In the hands of highly skilled technicians it functions as an asset to any investigation,” concludes Condon.