The Polygraph and How It Works

The term "polygraph" derives from the Greek words poly (many) and graph (writing) — "many writings". The name refers to the manner in which selected physiological activities are simultaneously collected, measured and recorded.

A polygraph is a scientific diagnostic instrument that is used by a polygraph examiner to administer a polygraph examination for the purpose of verifying the truthfulness of a person's statement regarding a specific issue - whether criminal, civil or private - that is the object of an investigation.

The polygraph is often called the "lie detector".

An examiner may use an analog polygraph, however, today, most polygraph examinations are administered using digital or computerized polygraph technology.

Before beginning a polygraph examination, the examiner will fasten various painless components to and around the examinee's body, thereby connecting him or her to the polygraph instrument. These components are equipped with sensors which serve to collect, measure and record, onto polygraph charts, the examinee's physiological data obtained from three major systems of the human body — i.e. i) the cardiovascular system (heart rate, blood pressure, blood volume); ii) the respiratory system (breathing patterns); and iii) the electrodermal system (sweat gland activity) — as he or she answers a series of questions pertaining to a specific issue during the course of a polygraph examination.

The polygraph is an instrument that is used to measure human physiology. It cannot think or judge. It is the job of the polygraph examiner to analyze, interpret and evaluate the examinee's physiological data collected during the examination and then to form a professional opinion based on the evaluation of this data.