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What is a Polygraph?

The word polygraph literally means “many writings

The polygraph is a diagnostic tool which records respiration, cardiovascular activity and electro dermal activity, the instrument itself is a combination of several recording devices routinely used in the medical and scientific community

Other names for the polygraph include ‘Psychophysiological detection of deception’ and ‘lie detector’. Whilst the polygraph is often termed a “lie detector”, this can be confusing as the polygraph instrument does not actually detect lies. The polygraph measures, through way a number of components attached to a subject, the physiological responses which occur when that subject is asked questions. This information (or tracing)s are recorded on charts which the examiner can interpret to make a determination as to whether or not the subject was being truthful when answering the questions.

A polygraph test will take a minimum of 1.5hours but may take up to three hours. The test comprises of three parts.

The first part is the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test. During this period, the examiner will discuss the questions to be asked and familiarize the examinee with the testing procedure.

The second part is the collection of charts , the examiner will administer and collect a number of polygraph charts. Following this, the examiner will analyse the charts and render an opinion as to the truthfulness of the person taking the test. The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions asked during the test. It is important to note that a polygraph does not include the analysis of physiology associated with the voice.

Finally the chart analysis and post-test interview concludes the process.

Use of the polygraph has been increasing generally in the U.K and Ireland and it is often used as part of an investigative process when either a crime or a suspected crime has been committed. This use is likely to continue to increase.