Jeremy Kyle’s lie detector’s reliability is questionable at best. Indeed, the validity of the lie detector test results has long been controversial – particularly since lie detectors don’t actually detect lies. Instead they detect the subject’s physiological responses to questions, which can be caused by both questions and nerves. There is no way to tell what these responses are caused by and therefore, the lie detector test accuracy is subjective.


How Accurate A Lie Detector Test?

Just how accurate is a lie detector test and is it even worth taking? There is no way to predict how accurate a lie detector is, but in the UK the general practice amongst firms who use polygraph testing is to accept 75% as accurate enough. The same percentage is accepted in cases of infidelity polygraph tests usually carried out by a private investigator.


Three Stages Of Polygraph Testing

In the UK, polygraph testing consists of three stages – pre-interview, interview and post-interview. The advantage of the first stage is that it can let the examiner – a private investigator or a police officer – to gauge the subject’s state of mind and nerves, which is reflected in the results. In cases of commercial polygraph testing, the concept can condition the staff to be more honest within the organisation. However, as stated above, a polygraph lie detector cannot technically detect a lie – it merely judges the accuracy of the subject’s answers by their physiological responses and galvanic skin responses (GSR). Therefore, the polygraph test results accuracy is not set in stone. These mixed results can lead to another disadvantage – waste of time and damage of the morale within the business.


Polygraph Testing Apparatus

The polygraph instrument mechanics have upgraded from the needles scribbling lines on charts. Today’s polygraph testing apparatus includes a machine with tubes, cables and wires which are connected to the subject’s body and evaluate the way the subject’s body responds to the questions asked by the examiner. The machine assesses physiological responses including heart rate and blood pressure, respiration and GSR. Changes in these responses are indicators of stress, and lying is quite stressful, which is what lie detectors measure. For example, a person’s blood pressure is elevated when he or she is stressed due to lying, and a professional polygraph test service provider would be able to detect that with their machine. The same rule applies to the heartbeat – the pulse rate goes up when the subject is stressed by a question, or in general.

The GSR measures electric conductance of the skin which changes by virtue of sweat glands when a person experiences a particular emotion associated with lies. The sweat glands are controlled by the central nervous system and the increased perspiration can result from stress and nerves. People generally experience nerves before and during polygraph tests, which is one reason why lie detectors are not the most reliable method of investigation, whether police or occupational.

It is impossible to say with certainty how to beat a lie detector. Most people cannot suppress the physiological responses to stress outlined above. However, these responses can work in favour of, as well as against the accuser due to many factors. A faulty machine can also produce the answers that do not correspond with the facts.