What is a Polygraph?

General Info · Who Uses · Accuracy · Safety · Reliability · Admissibility ·Results · Cost/Time

The term "polygraph" or commonly known as a “Lie Detector” literally means "many writings." The name refers to the manner in which selected physiological activities are simultaneously recorded. Polygraph examiners may use conventional instruments, sometimes referred to as analog instruments, or computerized polygraph instruments.

It is important to understand what a polygraph examination entails. A polygraph instrument will collect physiological data from at least three systems in the human body. Convoluted rubber tubes that are placed over the examinee's chest and abdominal area will record respiratory activity. Two small metal plates, attached to the fingers, will record sweat gland activity, and a blood pressure cuff, or similar device will record cardiovascular activity.

A typical polygraph examination will include a period referred to as a pre-test, a chart collection phase and a test data analysis phase. In the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test. During this period, the examiner will discuss the questions to be asked and familiarize the examinee with the testing procedure. During the chart collection phase, the examiner will administer and collect a number of polygraph charts.

Following this, the examiner will analyze the charts and render an opinion as to the truthfulness of the person taking the test. The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions asked during the test. 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 have scientific support.

Who uses polygraphs examinations?

Three sectors of society use polygraph examinations for various reasons and purposes.

Private Sector

Individuals, Couples and Families use polygraph examinations to verify statements and find out the truth on a variety of issues including infidelity, drug use, addictions, sex offenses, employee theft, criminal activities, abuse and all other matters.

Legal Community

Polygraph is used extensively by attorneys who wish to provide the best possible defense for their clients. Most attorneys will submit their own clients to the exam, while others will use the polygraph to verify statements made by witnesses and other parties to litigation.

Contrary to popular belief, polygraph is not per-se inadmissible in court proceedings. Admissibility standards are different in each jurisdiction. Some jurisdictions allow polygraph evidence, either stipulated or un-stipulated, some prohibit polygraph evidence altogether, and many others allow the judge to decide admissibility on a case-by-case basis. The Daubert case is presently the standard for the admission of scientific evidence, which includes polygraph. In reality, most polygraph results are used outside of the courtroom in pre-trial negotiations, plea bargaining, sentence recommendations, and witness verification or impeachment.

Law Enforcement Community

  • Law Enforcement, Federal Agencies, Military and Government
  • Local Police, U.S. Military Branches and Government Agencies such as the FBI, CIA, NSA and Department of Defense all use polygraph examinations for applicant screenings, criminal investigations and matters of national security.

How accurate is the polygraph?

U.S. Government studies have concluded that the single-issue (one question) polygraph exam, conducted properly by a qualified examiner, is 87 to 95 percent accurate. The Michigan State Police have also completed studies over the years and conclude their examinations are in the high 90 percentile. It is the most accurate tool available today for determining truth or deception. Accuracy of the multi-question exam drops to around 80 percent due to a number of psychological factors. These statistics do not include "inconclusive" results in which no opinion can be made from the polygraph charts, which happens up to about 20% of the time.

While the polygraph technique is not infallible, research clearly indicates that when administered by a competent examiner, the polygraph test is one of the most accurate means available to determine truth and deception.

What if the person has a medical condition?

A polygraph exam does not cause any direct injury to the person being tested. The only discomfort is a standard blood pressure cuff which goes on the arm (typically) and is inflated for less than five minutes at a time. There are increased stress levels during the testing process which should be considered. Some medical conditions are sensitive to increased stress levels, such as some heart conditions. Depending on the medical condition, most examiners would require an approval from the treating physician prior to conducting an exam on someone with such a condition.

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.

Can someone beat the test?

The polygraph works by recording changes in a person's Sympathetic Nervous System, part of the Autonomic Nervous System, which operates independently of conscious thought. For example, your lungs and heart continue to operate even when you are asleep - you don't have to think about it. These systems can be consciously controlled only very slightly, and attempts to change these systems are usually picked up by the examiners, who are trained to identify such things. It is highly unlikely that someone can alter the outcome of a polygraph exam, but it is not impossible. A verified accuracy rate as high as 95% attests to this fact.

Is the polygraph admissible in court?

Federal courts have ruled that polygraph is NOT per-se inadmissible in a court procedure, but that it may be considered when standard rules of scientific evidence have been met. In other words, applicants must apply to the judge for admissibility under the "Daubert" standard of evidence on a case-by-case basis. Individual judges can still decline to accept polygraph results, however. Each jurisdiction must be checked to determine admissibility standards. One of the greatest fears keeping polygraph evidence out of courts is the fact that such evidence would carry greater weight than other equally-important evidence and would tend to sway a jury in one direction even though other evidence may point the other way. In most cases, polygraph evidence is used during pre-trial negotiations and plea bargain agreements rather than during the trial itself.

What does it mean when someone "fails" a polygraph?

When a polygraph examiner concludes that deception is indicated to one or more of the subject's answers, the subject is said to have "failed" the exam. Deception is indicated when the person's autonomic nervous system displays a significant and repetitive "defensive" reaction to the relevant test question. Although this reaction in itself is not a "lie," years of research have found that 90-95% of persons who display this reaction were either lying to the relevant questions or were withholding pertinent information relating to these question. Frequently, an examiner will conclude only that "the subject can not be excluded as a suspect" when deceptive reactions are present. It is important to note that some persons will "fail" a polygraph even though they are telling the literal truth but continue to hold back pertinent or incriminating information from the examiner. We strongly suggest that no one make a life-altering decision based solely on the results of a "failed" polygraph test without the existence of additional evidence supporting this test result.

Capital Polygraph adheres to very strict confidentiality and privacy standards. All information from an examination is kept strictly confidential and private.

FAQ's provided by the American Polygraph Association

Cost and Required Time

On average a one issue polygraph examination lasts about two hours. The cost to conduct a polygraph examination ranges between $325.00 and $500.00.


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