About Polygraph

Lie Detection Experts Available Worldwide

GPN is the world’s oldest and largest referral service for private polygraph (lie detector) testing, offering services at more than 500 different testing locations worldwide. Our examiners are all graduates of APA Accredited training schools, are thoroughly screened and submit to Quality Control reviews before being considered for membership. Nearly half of the examiners submitting applications are denied membership for lack of qualifications or experience. Members must complete regular continuing education programs to ensure they are using the most up-to-date and validated techniques. Our clients will never be referred to an untrained or fraudulent examiner.


A polygraph used for the purpose of lie detection is an instrument that monitors and records various manifestations of the Sympathetic and Parasympathetic Nervous Systems while a series of carefully designed questions is asked of the person who is attached to the instrument.

These manifestations include changes in blood pressure, pulse rate, electro-dermal activity, and respiration, but may include additional components as well, such as blood volume monitors and motion sensors. The term “polygraph” derives from the Greek words poly (many) and graph (writing) ‘ “many writings”. The name refers to the manner in which selected physiological activities are simultaneously collected, measured and recorded.

A polygraph (a/k/a lie detector) is a scientific diagnostic instrument that is used by a polygraph examiner to administer a polygraph examination for the purpose of verifying the truthfulness of a person’s statement regarding a specific issue


In a specific issue test, using a validated technique, average accuracy will exceed 90%. The accuracy of a polygraph depends heavily on the following elements.

  • The specific technique used by the examiner
  • The examiner’s primary and continuing training (see How to Select an Examiner)
  • The number of relevant questions asked. In general, the more relevant questions asked the less accurate the results will be. Using only one relevant question will produce the highest level of accuracy that can be achieved. Most of the current research on polygraph is contingent upon the use of a “Specific Issue” format (one relevant question). Adding even one question to a specific issue test doubles the error rate.
  • Proper question design. Questions must be formulated correctly (see “Rules” below)

The American Polygraph Association has a compendium of research studies available on the validity and reliability of polygraph testing. The 80 research projects published by the APA since 1980 involved 6,380 polygraph examinations or sets of charts from examinations. Researchers conducted 12 studies of the validity of field examinations, following 2,174 field examinations, providing an average accuracy of 98%. Researchers conducted 11 studies involving the reliability of independent analyses of 1,609 sets of charts from field examinations confirmed by independent evidence, providing an average accuracy of 92%. Researchers conducted 41 studies involving the accuracy of 1,787 laboratory simulations of polygraph examinations, producing an average accuracy of 80%. Researchers conducted 16 studies involving the reliability of independent analyses of 810 sets of charts from laboratory simulations producing an average accuracy of 81%. The average accuracy for all 6,380 exams is 88%.

New industry standards require that a particular technique be at least 90% accurate (in specific issue testing) for that technique to be “validated.” Make sure your examiner is using a validated polygraph technique.

The actual make and model of polygraph equipment used is not nearly as important as the above-noted elements. A good examiner can provide reliable polygraph services using any calibrated polygraph instrument.


A validated testing technique is one that has been validated by the American Polygraph Association, though research, to achieve a minimum level of accuracy (90% for specific issue tests, 80% for multiple issue tests). Other techniques are less accurate and are not supported by scientific research.


If polygraphs don’t detect lies, then what do they detect?

People lie for a variety of reasons. Some are so-called “white” lies, like “You sure have a nice car.” Some are more serious, like “No, I didn’t rob that bank.” And then we have many lies in the middle range, such as “I have a great deal of experience working with this type of software.” In reality, very little takes place in the brain when we tell a lie. There is no such thing as a typical “lie response.” In other words, just because you tell a lie doesn’t mean you will have a reaction to it, and if you do, it will be a different reaction than someone else would have. So if polygraphs don’t detect lies, what do they detect?

Evolution has designed humans (and most animals) with a self-defense mechanism that is activated whenever we are threatened or placed in danger. For example, if you are walking along a path and come across a poisonous snake, your brain will have a reaction to that snake because you realize it could hurt you. This realization automatically triggers your body’s self-defense mechanism as it tries to help protect you. Within a few seconds some typical reactions occur: Adrenaline is released to improve your alertness, additional blood is sent to your muscles in case you need to defend yourself physically, your skin glands become more active in preparation for a physical response, your digestive process slows down, and your breathing changes. After this reaction takes place, you are better prepared to deal with the crisis you are faced with and can make a conscious decision about what to do.

What is more important than the lie itself is the reason for telling the lie. When we do something wrong, such as commit a crime or do something we know we shouldn’t have done, we realize that if we get caught that we will be punished. This punishment might be imprisonment, embarrassment, loss of a present or future job, loss of money, or loss of a relationship. Our instinct for self-preservation makes us want to avoid being punished for what we did. This is usually accomplished by lying.

In other words, lying in most cases is an act of self-defense. We usually lie to avoid punishment. Being caught in the lie means we will be punished. It is our understanding of the consequences that triggers the body’s self-defense mechanism when we lie. The polygraph instrument is a finely tuned diagnostic device which will record various aspects of your body’s Sympathetic and Parasympathetic Nervous Systems and will recognize when your body’s self-defense mechanism has been activated by lying. It isn’t the lie that makes a polygraph work, it’s the understanding that there are consequences to being caught in that lie. Our bodies create self-defense reactions to try to avoid those consequences.

Another operative element in polygraph testing is known as “cognitive dissonance.” People normally tell the truth. It requires no effort. When we lie, we must force ourselves to do so in conflict with what our bodies would normally do. This conflict within us creates a reaction because we have to consciously “fight” our body’s normal (truthful) responses, and the resulting reaction causes some of the changes seen with a polygraph instrument in deceptive people.


Click HERE to experience what it’s like to undergo a typical polygraph exam.


There are quite a few rules for designing proper polygraph questions. Your examiner will work with you to develop the best questions for your situation, but here are some of the basic rules for question design.

  • All polygraph questions must be answered with a “yes” or “no.” Narrative answers are not permitted. Normally, “no” answers are expected from suspects and “yes” answers are expected from victims and witnesses.
  • Questions can not be subjective or ambiguous. Each question must be interpreted the same way by any person who hears it. When in doubt, specific words or phrases can be defined and agreed-upon before the exam.
  • Lengthy questions are not permitted. A question that takes more than 6 or 7 seconds to ask (using normal speech) is too long.
  • Hypothetical questions are not permitted.
  • Questions about opinions, emotions, feelings, or the future can not be used. For example, examiners can not ask if someone loves you.
  • Compound (multi-part) questions are not generally used.
  • Questions about lying are not generally used. Polygraph questions are asked in the most direct way possible. For example, we would ask “Did you steal the missing wallet?” and not “Are you lying about stealing the missing wallet?”
  • Questions in the same exam must be related to one another. Examiners can not mix issues in a test. For example, an examiner can not ask questions about “stealing” and “using drugs” in the same exam. Each new issue requires a separate exam.
  • You can find a more comprehensive list of QUESTION DESIGN RULES by clicking HERE.


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 them. 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 significantly higher than 90% attests to this fact. Most examiners are now using “countermeasures detection” equipment which easily identifies anyone attempting to use the techniques taught by some web sites and government agencies. Unfortunately, many honest people are found “deceptive” to the test questions after attempting to use these techniques simply because they attempted to influence their test results. When an examiner discovers that the examinee is doing things to affect the charts, the result is either “deception indicated” or “inconclusive.” In other words, a person will not pass a polygraph by using these techniques. In fact, recent research (2008-2009) has determined that in most cases when someone attempts to use the techniques taught on the internet to “beat” a polygraph, their test results actually GET WORSE (their scores indicate greater deception than if they had done nothing). Use of certain drugs and medications can also affect the exam, but such use generally results in an “inconclusive” test. It is virtually impossible to change a result from “deceptive” to “truthful” through the use of drugs or medications prior to an exam. If drugs are suspected, a pre-test (or post-test) drug screening is advised.


Since a polygraph is actually several instruments combined into one, each component was developed independently of the others. These components were finally combined in 1938.

In 1878, science first came to the aid of the truthseeker through the research of Italian physiologist Angelo Mosso. It was then that Mosso used an instrument called a plethysmograph in his research on emotion and fear in subjects undergoing questioning and he studied the effects of these variables on their cardiovascular and respiratory activity. Mosso studied blood circulation and breathing patterns and how these changed under certain stimuli. The use of the plethysmograph revealed periodic undulations or waves in a subject’s blood pressure caused by the respiratory cycle in response to certain stimuli. Angelo Mosso was the first scientist to report on experiments in which he observed that a person’s breathing pattern changed under certain stimuli, and that this change, in turn, caused variations in their blood pressure and pulse rate.

The first use of a scientific instrument designed to measure physiological responses for this purpose came in 1895 when Italian physician, psychiatrist and pioneer criminologist Cesare Lombroso modified an existing instrument called a hydrosphygmograph and used this modified device in his experiments to measure the physiological changes that occurred in a crime suspect’s blood pressure and pulse rate during a police interrogation. Lombroso is accorded the distinction of being the first person to have used the instrument successfully as a means for determining truthfulness from deception in crime suspects.

In 1914, Italian psychologist Vittorio Benussi discovered a method for calculating the quotient of the inhalation to exhalation time as a means of verifying the truth and detecting deception in a subject. Using a pneumograph (a device that recorded a subject’s breathing patterns) Benussi conducted experiments regarding the respiratory symptoms of lying. He concluded that lying caused an emotional change within a subject that resulted in detectible respiratory changes that were indicative of deception.

Dr. William Moulton Marston, an American attorney and psychologist, is credited with inventing an early form of the lie detector when, in 1915, he developed the discontinuous systolic blood pressure test which would later become one component of the modern polygraph. Dr. Marston’s technique used a standard blood pressure cuff and a stethoscope to take intermittent systolic blood pressure readings of a suspect during questioning for the purpose of detecting deception.

In 1921, John A. Larson, a Canadian psychologist employed by the Berkeley Police Department, in California, developed what many consider to be the original lie detector when he added the item of respiration rate to that of blood pressure. He named his instrument the polygraph, a word derived from the Greek language meaning “many writings” since it could read several physiological responses at the same time and document these responses on a revolving drum of smoked paper. Using his polygraph, John A. Larson was the first person to continually and simultaneously measure changes in a subject’s pulse rate, blood pressure and respiratory rate during an interrogation. His polygraph was used extensively, and with much success, in criminal investigations.

In 1938, Leonarde Keeler further refined the polygraph when he added a third physiological measuring component for the detection of deception called the psychogalvanometer, a component that measured changes in a subject’s galvanic skin resistance during questioning, and in doing so, thus signaling the birth of the polygraph as we know it today. In 1939, Leonarde Keeler patented what is now understood as the prototype of the modern polygraph. Today, Leonarde Keeler is known as the father of polygraph.

In 1960, Cleve Backster, building upon John Reid’s Control Question Technique, developed the Backster Zone Comparison Technique (ZCT), a polygraph technique which primarily involved an alteration of the Reid question sequencing. Backster also introduced a quantification system of chart analysis, thus making it more objective and scientific than before. This system for the numerical evaluation of the physiological data collected from the polygraph charts has been adopted as standard procedure in the polygraph field today.

Withstanding more than a century of research, development and widespread use, the polygraph test remains the most effective means of verifying the truth and detecting deception.


Click HERE for a glossary of polygraph (lie detector) terms and abbreviations.


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