According to the Encyclopædia Britannica, the polygraph test or better known as lie detector test measures the blood pressure, pulse, and breathing pattern on a human subject when answering questions posed to them. A graph will show the movement of the vital signs. If it changes significantly, it indicates that the subject is lying.
The data obtained from the test is then used in making an assessment of whether or not the subject is lying. Lie detector test has been used in police interrogations and investigations since 1924.
Read: Suspects in cop murder case to take lie detector test
In terms of accuracy, the test is still controversial among psychologists and is not always legally admissible as evidence in court. This is due to examiner’s often subjective interpretation and because different people react differently to lies, thus the test is not a perfect tool and can be manipulated. (rr)