What is a polygraph?

The polygraph is a sophisticated, scientific instrument that is designed to measure and record human physiology.

There are two types of polygraph instruments; the analog, which is the type that most people are familiar with, has four to six metal pens and a moving paper graph that is also referred to as a chart; and the digital or computer polygraph that also has a graph which moves across the computer screen.

Both types have basic recording components that measure breathing pattern, perspiration levels, heart rate and blood pressure. Peripherals that attach to the body include two convoluted, rubber tubes that are placed around the chest and abdomen and measure breathing pattern; two metal finger plates that are attached to the index and ring finger of the same hand that measure perspiration levels and a blood pressure cuff similar to the type used in a doctor's office which measures heart rate and blood pressure.

Some examiners employ optional components but those mentioned here reflect the typical configuration of a polygraph instrument.

Both the analog and computer polygraph instruments have the same rate of accuracy and reliability.

Can a person beat the polygraph?

No.

Probably the most misunderstood aspect of polygraph examinations is the idea that someone can miraculously fool their own physiology or the scientific technology that is the polygraph instrument.

Unfortunately, this misconception is exaggerated by a small, unscrupulous group of people who will sell you their books and ideas on how to beat the polygraph examination. What these people are really selling is referred to in the polygraph community as counter measures, such as biting your tongue, placing a tack in your shoe, etc. What these peddlers don't tell you is that these counter measures produce abnormal, unnatural responses on the polygraph chart that are immediately obvious to the examiner. Polygraph examiners are thoroughly trained on counter measures.

When an examinee practices counter measures, there is an assumption that the person has something to hide and the examination is discontinued. In most cases, the examinee is considered to be deceptive.

Polygraph technology is based on the involuntary responses of the autonomic (automatic) nervous system. When a person tells a conscious lie, certain physiological changes take place in the body that cannot be controlled.

The polygraph instrument is designed specifically to measure and record these changes if and when they take place. When these changes do occur at particular points during the examination, deception may be indicated. Conversely, when a person is answering questions truthfully, there is a lack of any significant deceptive criteria and, therefore, no deception is indicated.

While there are numerous physiological changes that result from telling a lie, the polygraph instrument measures and records three of these parameters; pneumocentric (breathing pattern), electrodermal (perspiration levels) and cardiocentric (heart rate and blood pressure).

When operating properly, the polygraph instrument is 100% accurate in that it performs the tasks for which it is designed.

What is the accuracy rate of a polygraph examination?

The polygraph instrument itself is 100% accurate. In proper operating condition, the polygraph does exactly what it is designed to do -- measure and record human physiology. As is the case in all matters, when the human element is added, examiner and examinee, variables are introduced and the rate of accuracy is slightly reduced.

Reliable, impartial research on polygraph examinations, consistently show an accuracy rate of 97%. Therefore, 97 of 100 examinations conducted result in an accurate analysis. The remaining 3% consists mostly of inconclusive or indeterminate results and occasionally, false positive and false negative results.

Inconclusive results, means that there is not enough measureable data on the charts to make a determination of truth or deception. False positive results means that the examinee was truthful but was reported to be deceptive. False negative means the examinee was deceptive but reported as truthful.

How do I prepare for a polygraph examination?

-Get a good night's sleep.

-Avoid alcohol for at least 24 hours prior to the examination.

-Always avoid illegal substances.

-If you take prescription medicine do not alter your regimen or dosage. Tell your examiner about your medication. Most medicines will not affect the examination.

-Don't change your eating routine. Fasting is not necessary.

-Speak with your examiner about any concerns you may have. Polygraph examiners know that the best candidate for an examination is a person who is informed and comfortable with the process. We always welcome your questions.

-Do not attempt to force the results or help the examiner during the test. Your own physiology will do the work for you. If you try to control your physiological functions it may appear that you are attempting to beat the examination and this will certainly not help you.