Polygraph / Lie Detector Test

The polygraph works by tracing changes in a person’s physiological conditioning during questioning. These changes are recorded directly on to the polygraph charts in order that they can be reviewed. Some of the changes that occur may replicate those that have been linked with truth or deception for many years. These physiological changes have been the subject of various research projects and our examiners have undertaken many hours of polygraph chart analysis instruction to interpret them. The Polygraph charts are generated by attaching four components to the subject.

A Polygraph test will usually take between 2 / 3 hours, sometimes longer and consists of 3 phases; a pre-test interview, collection of charts, and analysis of charts. Polygraph tests are the most reliable technique to test if someone is being deceptive to a specific issue.

During the pre-test interview the examiner will explain how the polygraph works, discuss the issue and develop and review all questions to be asked on the polygraph test. This stage is normally the longest to complete, and can take anywhere between 45 and 90 minutes.

The examiner will construct questions from the information given regarding the test issue. He/She will review the questions with you before testing begins. All the questions should meet the strict rules for the latest polygraph techniques to ensure test accuracy.
All questions are discussed with the subject thoroughly before the test commences and will be answered with a “yes” or “no” answer only.

During this phase the subject will be attached to the polygraph. The set of questions that was developed during the pre-test interview will be asked on several occasions.

Once the examiner has collected the polygraph charts he/she will analyse the results before giving a decision as to the subject’s truthfulness or deception to the given issue.


A polygraph examination consists of three distinct phases:

I. Pre-Test Phase (Information Collection, Relevant Questions/Statements Formulation);
II. In-Test Phase / Polygraph Examination (Chart Collection);
III. Post-Test Phase (Data Analysis, Scoring Procedure).

I. PRE-TEST PHASE (Information Collection, Relevant Questions/Statements Formulation)

During this first phase the examiner will:

  1. obtain the examinee’s/client’s version of the facts regarding the specific issue under investigation;
  2. formulate and review with the examinee/client all the questions that will be asked during the polygraph examination.inform the examinee/client that the polygraph procedure will be audio and video recorded (for quality purposes and then deleted with all collected charts/ any personal information within 24 hours after the test completed for security purposes)
  3. complete the required paperwork;
  4. make sure the examinee understands why he or she is being asked to take a polygraph examination in the case concerned;
  5. answer any questions the examinee might have;
  6. advise the examinee of his or her constitutional rights, of his or her right to legal counsel, and of the voluntary action of submitting to a polygraph examination;
  7. provide the examinee with a detailed explanation of the polygraph procedure, as well as the polygraph instrument and its components;
  8. establish the examinee’s physical, psychological, and physiological history in order to determine whether he or she is fit to undergo a polygraph examination;


The polygraph examination takes place during this second phase. Just before beginning the examination, the blood pressure cuff will be inflated to a pressure of 60 mmHg. The examiner will then ask the examinee the series of questions that were formulated and reviewed during the pre-test interview. This series of questions will be asked a minimum of three times. As the examinee answers the questions, his or her physiological data are continuously collected, measured, and recorded by the polygraph instrument.

The examinee will have a relaxation period of approximately two minutes between each series of questions..

III. POST-TEST PHASE (Data Analysis, Scoring Procedure, Results).

During this last phase, the examiner will analyze and evaluate the physiological data by means of scientifically based numerical quantification system, and will render one of the following results:

No Deception Indicated: The examinee is telling the truth.

Deception Indicated: The examinee is not telling the truth.

Inconclusive: The evaluation of the examinee’s physiological data is inconclusive.
(less than 5% of all conducted tests).

The examiner will give the examinee the result of the polygraph examination and discuss this result with him or her. If the physiological data recorded on the polygraph charts show reactions on the part of the examinee to one or more of the questions asked during the polygraph examination, he or she will be given the opportunity to explain these reactions.


​The computerized polygraph instrument collects, measures, and records physiological data obtained from three major systems in the human body, all of which are controlled by the Autonomic Nervous System.

Cardiovascular System: Heart rate, relative blood pressure, blood volume;

Respiratory System: Respiratory activity;

Electrodermal System: Galvanic skin response, i.e., sweat gland activity.

Following the pre-test interview, the polygraph examiner will place various painless components on and around the examinee’s body, thereby connecting him or her to the polygraph instrument. These components are equipped with sensors that serve to collect the examinee’s physiological data as he or she answers the series of previously reviewed questions during the course of the polygraph examination.

The Sensors:

1) A standard blood pressure cuff applied to the examinee’s upper left arm for the purpose of recording cardiovascular activity;

​2) Two convoluted rubber tubes (called pneumographs), placed over the examinee’s chest and abdomen to record respiratory activity;

​3) Two small metal plates (called galvanometers), attached to the fingers of the examinee’s right hand to record Galvanic skin response, i.e., sweat gland activity;


Before beginning the polygraph examination, the examiner will administer a calibration test. The purpose of this test is threefold:

  • To find and fix examinee’s physiological baseline at the time of the test through which the expected nervousness or anxiety of the examinee will not affect the test.
  • ​To induce or to strengthen in the examinee the expectation that the polygraph can accurately determine the truthfulness of his or her answers;
  • To obtain adequate tracings of the examinee’s physiology to ensure that he or she is a suitable candidate to undergo a polygraph examination;
  • To confirm to the examiner that the polygraph instrument is in good working order at the time of the polygraph examination;


​All polygraph examinations are administered by BPS Examiners in accordance with the Code of Ethics and the set of Standards and Principles of Practice required by the American Polygraph Association (APA) – the world’s leading association dedicated to the use of evidence-based scientific methods for credibility assessment.