Lie detection, is it true?

A lie detector or polygraph machine is used to aid in finding out if someone is truthfully answering a specific set of questions. It is a combination of various devices used to measure a person's physical responses to what are known as irrelevant, control and relevant questions. How this data is interpreted by the examiner will determine if the subject is telling the truth.

In a typical lie detection test the subject is asked a number of question before the actual test is performed. These are used to create what is known as a "baseline". How the subjects reaction to these question will help create the baseline. The subjects pulse, blood pressure, rate of breathing and how much they sweat could be all measured as physical responses to help create the baseline. When the actual test questions are asked the response to these questions is compared to the questions asked to create the baseline.

There are three types of questions asked. Some questions are irrelevant such as asking the subject what their name is. Others are called probable-lie control questions and often get an answer which is not truthful. This type of question could be asking the subject if they ever committed a crime. The type of question most important to the examiner is what is known as a relevant question. A relevant question would be like asking the subject if they committed the crime. If the subjects response to the probable-lie control question is greater than to the relevant questions, then the answer to the relevant question is considered truthful.

It should be noted many scientists do not consider a lie detector test to be very accurate. It is not considered scientific by many and therefore not accurate enough to be used in a court of law.