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What is a Polygraph?

The term "polygraph" literally means "many writings." The name refers to the manner in which selected physiological activities are simultaneously recorded. Polygraph examiners my use conventional instruments, sometimes referred to analog instruments, or computerized instruments. It is important to understand what a polygraph examination entails. A polygraph will collect physiological data from at least three systems in the body.


Corrugated rubber tubes (or electronic sensors) placed over the examinee's chest and abdominal area will record respiratory activity. Two small metal plates or disposable adhesive electrodes, attached to the fingers, will record sweat gland activity, and a blood pressure cuff or similar device will record cardiovascular activity. Some instruments also monitor other activity. For example, a finger plethysmograph, which monitors blood volume in a fingertip, or motion sensors, which monitor general movements that might interfere with test data, are often used. 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 stress are not polygraphs and have not been shown to work any better than chance (i.e. accuracy is similar to making a decision based on a coin toss).

What happens during a polygraph test?

A typical polygraph examination will include a period referred to as a pre-test interview, a chart collection phase and a test data analysis phase. During the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test, answering any questions the examinee might have. It is during this phase that the examiner will discuss the test questions and familiarize the examinee with the testing procedure. During the chart collection phase the examiner will administer and collect a number of polygraph charts. The number of questions and the number of charts will vary, depending on the number of issues and technique employed. Following this, the examiner will analyze the charts and render an opinion as to the truthfulness of the examinee. The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions presented during the test.

How long does a test take?

Any polygraph exam should take a minimum of an hour and a half to two hours to complete.  This is because the examiner needs to properly explain the testing procedures to the examinee.

Who uses the polygraph?

The four sectors that use the polygraph include law enforcement agencies, the legal community, government agencies, and the private sector. They are further described as follows:


• Law Enforcement Agencies

- Federal law enforcement agencies, state law enforcement agencies, and local law enforcement agencies such as police and sheriff's departments.


• Legal Community

- U.S. Attorney Offices, District Attorney Offices, Public Defender Offices, defense attorneys, Parole & Probation Departments.
- The court systems in cooperation with probation and parole officers and therapists to monitor convicted sex offenders.- Attorneys in civil litigation.


• Government Agencies

- Department of Defense Agencies
- Agencies in the Intelligence Community


• Private Sector

- Companies and corporations under the restrictions and limitations of the Employee Polygraph Protection Act of 1988 (EPPA).
- Private citizens in matters not involving the legal or criminal justice system.

Who gets the results?

According to the various state licensing laws and the American Polygraph Association's Standards and Principles of Practice, polygraph results can be released only to authorized persons. Generally those individuals who can receive test results are the examinee and anyone specifically designated in writing by the examinee, the person, firm, corporation or governmental agency that requested the examination, and others as may be required by law.

How accurate is a polygraph exam?

There are different types of techniques that can be used during a polygraph exam.  The technique used by the examiner will be determined on the type of testing that's being conducted.  With that, different techniques have different accuracy ratings.  Reasearch shows that polygraph examinations have an accuracy rate of up to 97%.


As with any test involving humans, there is always a possibility of error, this is why polygraph exams are not 100% accurate.  In fact, no test is 100% accurate.  Human error exists with any test.  


For a polygraph test, the human error could be one or a combination of things.  Errors could be because the examiner fails to properly prepare the examinee for the examination.  This is why exams should last at least an hour and a half.  Another example of error could be the examiner misreading the physiological data on the polygraph charts.


Since it is recognized that any error is damaging, examiners utilize a variety of procedures to identify the presence of factors which may cause errors or an unbiased review of the polygraph records.


(Information obtained from the American Polygraph Association)