Polygraphs
General Information About the Polygraph Exam
What is a Polygraph?  
A polygraph examination is a scientific test that collects physiological data from a person with the purpose of detecting reactions associated with dishonesty. At least three systems in the human body are recorded during a polygraph examination. Respiratory activity is monitored by placing rubber tubes across the examinee's chest. Electro dermal or "sweat gland" activity is recorded by placing two small attachments to the fingers or palm of the hand. And cardiovascular activity is collected by a blood pressure cuff or similar device. It is important to note that a polygraph does not include the analysis of physiology associated with the voice. Instruments that claim to record voice or psychological stress are not polygraphs and have not been shown
to have scientific support.
 
Why are polygraph examinations used?
Polygraph exists to protect the public by verifying the truth and determining deception. Polygraphs are most commonly used for criminal and civil matters, government pre-employment screening, homeland security, commercial theft investigations and to monitor convicted sex offenders being supervised by probation and parole, and while under treatment.
 
Who uses polygraphs?
Polygraph exams are used by federal, state and local law enforcement agencies, U.S. and district attorneys offices, public defenders, lawyers, and parole and probation departments worldwide. Private and public companies also use polygraph examinations when authorized under the Employee Polygraph Protection Act of 1988 (EPPA).
 
Can a person fail a polygraph because of high blood pressure or nervousness?
No. Polygraph is not designed to record or measure nervousness. While a person's heart beat and respiration rate may increase when he or she is nervous, a qualified examiner understands this, and will take it into consideration when evaluating an examinee's response. Unlike general nervous tension, an examinee's reaction to deceptive responses is highly specific. An examiner mitigates a nervous response by reviewing the questions with the examinee and through an acquaintance or ""practice test" prior to the exam.
 
How reliable and accurate are polygraph exams?
While the polygraph technique is not infallible, research clearly indicates that when administered by a competent examiner, the polygraph test is the most accurate means available to determine truth and deception. Since 1980, a compendium of research studies -- encompassing 80 research projects, involving 6,380 polygraph examinations, and 12 studies of the validity of field examinations following 2,174 field examinations -- indicate an average accuracy rate of 98%.
 
Are polygraph exams admissible in court?
Contrary to popular belief, polygraph results are admissible in most courts across the country. The Supreme Court has yet to rule on the issue of admissibility so it has been up to individual jurisdictions to allow or disallow them. Most jurisdictions allow them if both the plaintiff and the defendant have agreed to have the results of the test be admissible, prior to the examination being conducted.