What is a polygraph (lie detector test)

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 analog instruments, or computerized instruments. It is important to understand what a polygraph examination entails. A polygraph will collect physiological data from at least three systems in the body:

Corrugated rubber tubes (or electronic sensors) placed over the examinee's chest and abdominal area will record respiratory activity. Two small metal plates or disposable adhesive electrodes, attached to the fingers, will record sweat gland activity, and a blood pressure cuff or similar device will record cardiovascular activity. Some instruments also monitor other activity. For example, a finger plethysmograph, which monitors blood volume in a fingertip, or motion sensors, which monitor general movements that might interfere with test data, are often used. 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 work any better than chance (i.e. accuracy is similar to making a decision based on a coin toss).

A typical polygraph examination will include a period referred to as a pre-test interview, a chart collection phase and a test data analysis phase. During the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test, answering any questions the examinee might have. It is during this phase that the examiner will discuss the test questions and familiarize the examinee with the testing procedure. During the chart collection phase the examiner will administer and collect a number of polygraph charts. The number of questions and the number of charts will vary, depending on the number of issues and technique employed. Following this, the examiner will analyze the charts and render an opinion as to the truthfulness of the examinee. The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions presented during the test.