Lie detectors have been controversial since their introduction nearly a century ago. With scientific studies producing mixed results, the controversy shows no sign of abating. Their use in the workplace is restricted by both federal and state laws.

How a Polygraph Works

Polygraph technology is based on the certain involuntary physiological changes people tend to undergo when they are telling a lie. A polygraph examination uses between four and six sensors attached to the subject’s body. The sensors are connected to a machine that monitors respiration, pulse rate, blood pressure and perspiration. Several control questions are asked in order to establish the subject’s baseline measurements before the examiner moves on to the questions of interest. The polygraph machine records the physiological data and later, the examiner reads the report to find the telltale signs of deceit.


Beating the Machine

Because the polygraph machine solely measures physiological responses, many experts believe that the system can be successfully fooled. Placing tacks in shoes or pins in the mouth allows the subject to raise the physiological response to control questions. Likewise, taking anti-anxiety medications or using relaxation techniques may depress the physiological response to target questions.

Reliability of the Polygraph

The National Academy of Sciences reviewed the research on the reliability of polygraphs in 2003. The Academy cited studies finding both types of possible errors, falsely indicating deception and failing to detect deception, occurring roughly 10-20% of the time, but concluded that “The evidence does not allow any precise quantitative estimate of polygraph accuracy.” In particular, the Academy noted that accuracy might be affected by personality type, sociodemographic group, psychological and medical conditions, examiner and examinee expectancies, different ways of administering the test, and countermeasures.

Employee Polygraph Protection Act

Polygraph testing can sometimes used in private employment. However, the Employee Polygraph Protection Act of 1988 has put several controls on its use. As a general rule, private employers may not perform a polygraph test as a condition of employment, nor may an employer inquire about the results of a polygraph test. Employees may not be discharged or disciplined for refusing to take a polygraph test or disclose the results of such testing.

However, the EPPA does not cover federal, state or local governments. Additionally, private sector security firms and pharmaceutical companies are permitted to perform testing on job applicants. Private employers are also permitted to test employees that are suspected of theft or embezzlement that causes direct financial injury to the employer.

When polygraph testing is permitted, it is strictly regulated. The examiner must be licensed and bonded and must follow stringent guidelines in every phase of the process. There are also strict limitations on disclosure of results.

State Laws

Many states have passed laws that further restrict the use of the polygraph. For example, California law does not permit any polygraph testing by an employer within the state except in federal, state and local governmental agencies. New York law goes even further, prohibiting all polygraph testing for employment purposes within the state, with no exceptions.