How does a Polygraph Test Happen?

Polygraph tests are not things to make fun of. Lie detector testing is the process of verifying the truthfulness of statements made by persons of interest. These statements are often part of an investigation and it is important that lie detector tests establish the truth behind them.

Device Components

A typical polygraph test machine has three major components, namely the blood pressure cuff, the pneumographs, and the galvanometers.

  • Blood pressure cuffs are attached around the upper arm of an examinee. It covers the branchial artery and provides a continuous tracing of the person’s cardiovascular activity such as his heart rate, blood pressure, and blood volume.
  • Pneumographs are the two rubber tubes fastened around the person’s chest and abdominal areas. These tubes are used to monitor his respiratory activity during the test.
  • Galvanometers are the two protruding electrodes attached to the client’s fingers. These components are used to obtain a reading of the client’s electro-dermal activity during the lie detector testing.

These components collect, measure, and record the different physiological data that the examinee registers during the course of the polygraph testing process. The data is recorded in the polygraph, helping the examiner determine the truth behind the answers.

Polygraph Phases

A typical polygraph test has three distinct phases. Each phase in the lie detector testing process is done scientifically and as accurately as possible.

The three lie detector phases are:

  • Pre-test Phase

During the pretest phase of the lie detector testing, the examiner begins with establishing a relationship with the client. He informs the client about the particular topic that is being investigated and of which he is a central figure.

The examiner will remind the client of his constitutional rights. He would also be reminded that he has the right to an attorney. Furthermore, he will also be reminded before the start of lie detector testing, that he is undergoing the test voluntarily and on his own free will. Proper documentation is needed in this phase to comply with the legalities.

The examiner will then go through the machine and the process with the client. He will explain the different procedures and will clarify the uses of the various components. If the examinee has questions, the examiner will answer the queries in this phase.

The examiner will then obtain the examinee’s version of the facts based on the issue being investigated. He will then endeavor to formulate and review with the examinee all the questions that will come up during the lie detector testing.

Once the client has assented to the examiner, a stimulation test will be performed. This is a calibration test to determine that the polygraph is working in good order during the time of the examination. This would demonstrate to the examinee that he or she is suited to undergo the polygraph technique.

  • In-Test Phase

The polygraph testing is done in the in-test phase. The examiner will conduct a number of tests – a minimum of three and a maximum of six tests. These tests last approximately five minutes each. During the test administration, the polygraph continuously records the physiological data onto the polygraph charts.

Examinees are allowed to have a two-minute rest break between tests. This is to ensure that the examinee is ready and able to move on with the lie detector testing.

After the tests are finished, the physiological results are analyzed, interpreted, and evaluated by the examiner. The examiner, using his expertise and other measures, will determine what the final professional opinion on the test is.

  • Post-Test Phase

The examiner will give the result of the polygraph test during the post-test phase. The examiner will give an opportunity for the client to explain himself on recorded reactions that he deems to be contestable.

The examiner then forms his opinion about the recorded physiological results. A verbal appraisal of the test would be given followed after some time by a written report. The written report contains a factual retelling of the procedure as well as the professional opinion of the examiner.

Professional Opinions

 There are only four accepted professional opinions during lie detector testing. They could either be NDI (No Deception Indicated), DI (Deception Indicated), INC (Inconclusive) or NO (No Opinion).

An NDI result means that there were no recorded deceptive reactions during the test and the examinee is telling the truth. A DI result shows that the examinee is not being entirely truthful. An INC result, meanwhile, means that the examiner cannot conclusively give his opinion. An NO verdict means that the charts are too distorted to provide an accurate opinion.

Accepted Methodologies and Strategies

Lie detector testing examinations are performed using the Limestone Polygraph Professional Suite or the Lafayette LX4000. These are the top-caliber systems of computerized polygraph technology in the industry today.

Examiners are also bound by the Standards of Practice and the prevailing Code of Ethics as required by various Polygraph Associations.

Polygraphs are also scored using a numerical-scoring system. These results are further subjected to a software program to validate the recorded charts.


Undergoing lie detector testing is not a procedure you would want to mess with. Polygraphs provide accurate readings that would help to thresh out information needed to establish the truth. Increasingly better technology now decreases the chances of fooling a polygraph. Better testing procedures are also being established to ensure the reliability of lie detector testing. A number of reputable lie detection companies can be hired to do the job the right way and give you the answers that you are looking for.


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