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Polygraph Examiners


Automatic body functions such as breathing and blood circulation are the basis for measuring individuals' truthfulness. There is no one physiological response that reveals a lie. However, the rates of nonvoluntary processes change in response to stress, and stress is likely to increase when an individual is lying. One of the first attempts to use this knowledge to detect deception was made in 1898, when suspected criminals were interrogated while their pulse rates and blood volumes were monitored. Tests conducted in 1914 measured the volume of the air that test subjects breathed, and tests performed in 1917 showed that changes in blood pressure also could indicate whether the subjects were telling the truth.

John A. Larson, a medical student who worked with a local police department, invented the first modern lie detector in 1921. Larson's instrument continuously recorded blood pressure, pulse rate, and respiration. His machine was called a polygraph, which means "many writings," because it recorded all these processes simultaneously. Later polygraphs incorporated galvanic skin reflex testing, which recorded the changes in the electrical conductivity of the skin resulting from changes in perspiration levels.

Polygraphs have been used in police intelligence and security investigations since 1924. Lie detector testing has sparked a great deal of controversy. Many people object to such testing as an invasion of privacy and a violation of civil liberties. The validity of polygraph tests has often been questioned, and test results are generally inadmissible in court unless the defense, prosecution, and judge agree to their use. While studies have rated the validity of polygraph examinations at 80 to 98 percent, their reliability depends on the skill and experience of the examiner.

This controversy resulted in federal legislation. In 1988, the federal government established the Employee Polygraph Protection Act, which placed strict controls on the use of polygraph testing by private employers. Businesses are prohibited from requiring polygraph testing of employees or job applicants, except for employers engaged in security services, toxic waste disposal, or controlled substances, and employers under contract with the federal government. Polygraph testing is also permitted when an individual is suspected of committing a finance-related crime.