A polygraph is an instrument which simultaneously measures and records certain physiological changes in the human body to determine whether a person is truthful or deceptive. The polygraph instrument collects Forensic Psycho Physiological data from at least 3 different systems in the human body.
- Convoluted rubber tubes, called "pneumograph tubes" records respiratory activity. These tubes are placed over the subject's chest and abdominal area.
- Two metal plates, called the "galvanograph" are attached to two of the subject's fingers, and will record the sweat gland activity.
- A blood pressure cuff called a "cardiograph" attached to a subject's upper arm will record cardiovascular activity (heart rate and blood flow)
The polygraph examination process consists of the following three phases:
During the Pre-Test interview the examinee is informed of his rights, he is asked to sign a polygraph consent agreement after it is been explained that the polygraph is a voluntary process. The polygraph examiner will then do an objective appraisal about the examinee’s physical and mental suitability. The instrument will be explained to the examinee and the questions which will be asked in the examination will be reviewed with the examinee.
The In-Test phase is when the polygraph examiner collects the Forensic Psycho Physiological Data while the examinee is asked to answer certain questions.
During the Post Test interview the examiner will evaluate the forensic data by means of the numerical quantification of the forensic data, and one of the following results can be determined:
- No Deception Indicated (Examinee was truthful on the relevant issue
- Deception Indicated (Examinee was deceptive on the relevant issue)
- Inconclusive (No opinion)
The examinee will be given the result and an opportunity to explain his physiological responses to the relevant questions if any were detected.
During the last 75 years more than 250 research field studies on the accuracy of polygraph examinations have shown that when a well trained polygraph examiner who utilize an accredited polygraph testing procedure the accuracy in the 98% range is.
The polygraph is therefore the most accurate method available to establish truth and deception.