Derived from the Greek language, the term "polygraph" means "many writings". The name refers to the way in which certain physiological activities are continuously and simultaneously recorded.
A polygraph is a diagnostic instrument used by a polygraphist to collect, measure and record certain physiological activities when a person answers a series of questions about a specific event during a polygraph examination. This physiological data will be analyzed to determine if the person was telling the truth when answering the polygraph examination questions.
Sometimes a polygraphist may use a conventional instrument, also called an analog instrument. However, since the early 1990s, most polygraph examinations are administered using computerized polygraph instruments.
Conventional instruments record physiological reactions continuously and simultaneously in graphic form using ink pens on a moving paper roll.
The development of medical grade instrumentation and software has made it possible for computerized polygraphs to record physiological data directly to a software program and display the data on a computer screen. Graph analysis is done on a screen, rather than on a roll of paper, and can be printed as well.
During a polygraph examination, the polygraph detects, measures and records physiological data obtained from three major systems in the human body, each of which is controlled by the Autonomic Nervous System:
A) Cardiovascular system: Heart rate, blood pressure, blood volume.
B) Respiratory system: Respiratory activity.
C) Electrodermal system: Activity of the sweat glands.
The polygraph is used to detect and record human physiology. It is the job of the polygraphist to analyze, interpret and evaluate the physiological data obtained from the polygraph examination and then form a professional opinion as to the truthfulness of the statements made by a person based on the evaluation of these data.
The polygraph is often called the "lie detector".
Polygraph examinations have gained widespread acceptance in the scientific fields of psychology and psychophysiology, the disciplines devoted to credibility assessment. Research conducted by the scientific community, government agencies, and independent universities clearly indicates that a polygraph examination, when properly administered by a professional and competent polygraph examiner using federal procedural and instrumentation standards, has a high degree of accuracy in verifying truth and detecting deception.
According to Dr. David C. Raskin, a world-renowned expert and prominent scientist in the field of polygraphy, the scientific data regarding the validity of the polygraph can be summarized as follows:
"High-quality scientific research conducted in the laboratory and in the field converge on the conclusion that a well-administered CQT (Comparative Question Test) is a highly accurate discriminator of truth-tellers and deceivers. Research results converge on an accuracy estimate that exceeds 90%."
According to the American Polygraph Association, 80 research projects, including laboratory and field studies, have been conducted and published since 1980 on polygraph validity and reliability. These projects involved approximately 6,300 polygraph examinations. In the 23 studies conducted in the field, the accuracy of polygraph tests was estimated to be 95%. In the 57 studies conducted in laboratory simulations, the accuracy of the polygraph tests was estimated to be 81%.
Like any other scientific instrument used to measure human physiology to form professional opinions, the polygraph is not infallible. However, the scientific community recognizes that polygraph examinations have a high evidentiary value in distinguishing truthful individuals from those who are deceptive and that no other alternative technique exists that works better to verify truth and detect deception.
No. Some people fear getting an electric shock from being connected to the polygraph instrument. Be confident that there is no possibility for this. The only sensation that people feel is a slight pressure on the left arm due to the blood pressure cuff that is applied to that area and inflated for 3 to 5 minutes when the questions are asked. The blood pressure cuff is the same one used by your doctor and nurses to measure your blood pressure.
No. In order for a polygraph examination to be administered correctly, the polygraphist will ask you to remain calm and not move unnecessarily while the examination is in progress. He or she will also ask you to breathe normally, not to take deep or shallow breaths, not to hold your breath or change your breathing, as such maneuvers can cause problems when analyzing the polygraph data. Since the polygraphist needs your full cooperation in this regard, you must agree to undergo a polygraph examination.
If you do not wish to undergo a polygraph examination, you may exercise your right to refuse.
It is normal for an innocent person to feel nervous about taking a polygraph examination and the skilled polygraphist is aware of this fact. The nervous reactions that are recorded on the tracings are not interpreted by the polygraphist as a manifestation of deception, because such tracings are completely different from those that are recorded when a person deliberately lies.
Once the polygraph examination is underway, the polygraphist will want you to be as comfortable as possible. To this end, he or she will do his or her best to reduce your level of nervousness before beginning the polygraph examination.
Although the polygraph measures and records blood pressure, high blood pressure does not cause physiological responses similar to those obtained when a person lies. Specifically, a lie represents a different curve than that caused by hypertension. A truthful response is obvious to the polygrapher even if the person has high blood pressure.
Please inform the polygraphist if you are being followed by a health care professional for hypertension or any other medical condition.
Antidepressants - such as Lithium, Prozac, Valium, Xanax and Beta blockers - may affect the outcome of the polygraph examination in that an inconclusive result may be obtained. However, for some people, such drugs would have no effect on the outcome of the polygraph examination. Contrary to some beliefs, drugs and prescription medications do not allow a person to "beat" or falsify the result of a polygraph examination.
During the pre-polygraph interview, the polygraphist will verify the person's physical, psychological and physiological history as well as any medications taken to ensure that the person is fit to undergo a polygraph examination.
Yes, during the pre-test interview, the polygraphist will review with you all the questions that will be asked during the polygraph examination. No trick questions will be asked during the exam.
A polygraph examination takes approximately two hours. Some may last longer or shorter depending on the complexity of the event under investigation. The examinations are recorded on audio and video tapes.
Yes, you will be informed of the results of your polygraph examination as soon as the tracings have been analyzed and evaluated. The polygraphist will then take the time to explain the results to you. If the physiological data shows any reaction on your part to one or more of the questions, you will have the opportunity to explain these reactions.
Since the early 1990's, most polygraph examinations are administered with the use of computers. The computerized polygraph instrument and its components continuously and simultaneously collect, measure and record physiological data from three major systems in the human body (cardiovascular, respiratory and electrodermal), which are controlled by the autonomic nervous system. These data will be analyzed and evaluated, and a professional opinion will be rendered by the polygraphist as to the truthfulness of the person's response to the relevant questions asked during the polygraph examination.
A polygraph examination consists of three steps:
1) Pre-test polygraph interview (Information gathering).
2) Polygraph examination (Data collection).
3) Post-Polygraph Interview (Data Analysis).
For more information on this issue please see the Polygraphic Procedure page.
Polygraph examinations are used in over 50 countries by government agencies, law enforcement, private security, legal, corporate and private sectors.