What is a Polygraph Test?

  • Pre-test interview & formulation of questions
  • Collection of Charts
  • Analysis of Charts


Will I know the questions to be asked on the polygraph examination?


How reliable is Polygraph Testing?


How Does the Polygraph Work?

  • Pneumograph
  • G.S.R.
  • Cardiosphygmograph

What is a Polygraph Test?

A Polygraph test will normally take between 2 to 3 hours, sometimes longer

The term "polygraph" literally means "many writings." The name refers to the manner in which selected physiological activities are simultaneously recorded. Polygraph examiners may use conventional instruments, sometimes referred to as analog instruments, or computerized polygraph instruments. It is important to understand what a polygraph examination entails. A polygraph instrument will collect physiological data from at least three systems in the human body. Convoluted rubber tubes that are placed over the examinee's chest and abdominal area will record respiratory activity.

Two small metal plates, attached to the fingers, will record sweat gland activity, and a blood pressure cuff, or similar device will record cardiovascular activity. A typical polygraph examination will include a period referred to as a pre-test, a chart collection phase and a test data analysis phase. In the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test. During this period, the examiner will discuss the questions to be asked and familiarize the examinee with the testing procedure.

During the chart collection phase, the examiner will administer and collect a number of polygraph charts. Following this, the examiner will analyze the charts and render an opinion as to the truthfulness of the person taking the test. The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions asked during the test. It is important to note that a polygraph does not include the analysis of physiology associated with the voice. Instruments that claim to record voice stress are not polygraphs and have not been shown to have scientific support

Pre-test interview & formulation of questions

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. 

Collection of Charts

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. 

Analysis of Charts

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

Will I know the questions to be asked on the polygraph examination?

Yes! 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. 




How reliable is Polygraph Testing?

The American Polygraph Association believes that scientific evidence supports the high validity of polygraph examinations. Thus, such examinations have great probative value and utility for various uses in the criminal justice system. However, a valid examination requires a combination of a properly trained examiner, a polygraph instrument that records as a minimum cardiovascular, respiratory, and electrodermal activity, and the proper administration of an accepted testing procedure and scoring system.

The American Polygraph Association has a compendium of research studies available on the validity and reliability of polygraph testing. The 80 research projects listed, published 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%. Tables list the authors and years of the research projects, which are identified fully in the References Cited.

Surveys and novel methods of testing are also mentioned. Spiral-bound copies of this article may be purchased for $25.00 postpaid from the American Polygraph Association:National Office 951 
Eastgate Loop, Suite 800 
Chattanooga, TN 37411-5608 
(423)892-3992 or 1-800-272-8037. 


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How Does the Polygraph Work?

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. 

Pneumograph

Two convoluted rubber pneumograph tubes are placed around the subject's upper chest and abdomen on the outside of their clothing, these record respiration and movement. 

G.S.R.

The GSR or Galvanic Skin Response is monitored by placing two finger plates across fingers, or two adhesive sensors directly on the hand. These plates trace changes to the skin resistance during the examination. 

Cardiosphygmograph

This component traces changes to the subjects relative blood pressure and pulse rate and it is similar to the pressure cuff your doctor uses when taking your blood pressure. Alternatively a finger blood pressure cuff may be used.

After the polygraph test has been completed the examiner will read and review the generated charts to establish the test results. The agreed questions will always be asked a minimum of twice before results can be determined.

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