A lie detector or
polygraph machine is used to aid in finding out if someone is
truthful answering a specific set of questions. It is a combination of various
devices used to measure a person's physical response to what is 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 questions before the actual
test is performed. These are used to create what is known as a baseline
How the
subject’s reaction to these questions 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 subject’s 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