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4 Main Analyses in Polygraph Studies

Though we came to know about the biomedical instrument Polygraph a lie detector used mostly in police investigations and examinations for certain jobs whether the person is giving true details or not? When answering certain questions but how it works?

In simple words below here..,


A polygraph is a machine in which the multiple ("poly") signals from the sensors are recorded on a single strip of moving paper ("graph").

How it works?
Chiefly 4 to 6 sensors are attached to body parts of a person during polygraph test and the sensors usually records
Breathing rate
Pulse rate
Blood pressure

And on certain cases records of arm and leg movement will also be taken into the account.

Polygraph Test:

The polygraph test starts with the 3 or 4 simple questions to establish the norms for the person's signals.

Then the real questions being tested by the polygraph are asked. Throughout questioning, all of the person's signals are recorded on the moving paper.

Both during and after the test, a polygraph examiner can look at the graphs and can see whether the vital signs changed significantly on any of the questions.

In general, a significant changes such as:

Faster heart rate
Higher blood pressure
Increased perspiration

->Indicates that the person is Lying.

However, when a well-trained examiner uses a polygraph, he or she can detect lying with high accuracy. However, because the examiner's interpretation is subjective and because different people react differently to lying, a polygraph test is not perfect and can be fooled.

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