Facts About Polygraph Testing

A polygraph test, also known as a lie detector test, uses a person's vital signs to attempt to determine whether the person is lying when answering a series of questions. A polygraph often is used in legal settings, but because of its inability to establish for a fact that someone is lying, it is not admissible in court.

Sensors

Polygraphs feature four to six sensors that are connected to the person submitting to the test. The four standard variables to be measured are pulse, blood pressure, rate of breath and volume of perspiration, but some machines also measure movement of the legs and arms.

Questioning

At the beginning of a polygraph test, the examiner asks a few general questions, such as the person's name or what color shirt the person is wearing. This introductory set of questions is administered to establish a base line for the person being questioned, allowing the tester to distinguish between a person with a bad case of nerves and someone who is lying. After this control level is set, the hard questions begin. The tester analyzes the results as they are recorded on a piece of moving paper during the questioning.

Uses

Polygraph tests are used in a variety of settings. Polygraph tests are used by many attorneys before going to trial to help them understand the strength of their case. They might use these tests to attempt to prove, for their own knowledge, their clients' guilt or innocence in order to make sure that a person's statements are valid before introducing him as a witness. Government agencies often use polygraph testing as a part of the employment application process because of the sensitive materials that these applicants will have access to. Individuals in the private sector also occasionally use polygraphs to expose secrets such as infidelity.

Polygraph Reliability

The debate has raged for years about whether polygraphs are reliable. They are not allowed in most state and federal courtrooms, but their use in other governmental settings continues to raise this question. While some scientists rate the validity of polygraph tests at 90 percent, which would still allow 10 percent of those tested to be wrongfully accused of lying. Others, most notably some psychologists, have rated the polygraph's reliability at 60 percent, which is not significantly better than a coin toss.

Employee Polygraph Protection Act (EPPA)

The Employee Polygraph Protection Act is a federal law enacted in 1988 that places strong restrictions on when and how an employer can subject an employee to a polygraph test. Intended only as a set of guidelines for the private sector, the EPPA also has a number of exceptions for companies that work for the federal government or handle sensitive materials, such as nuclear waste.

References

• How a Polygraph Works
• Polygraph FAQ
• Polygraph Debate