Employers use different tests to screen prospective employees. One of the most notorious tests is a lie detector or polygraph test. A lie detector test combines interrogation methods with physiological measurements to obtain information. The polygraph equipment usually records such phenomena as respiration, heart rate, blood pressure while a candidate is responding to a series of “yes/no” questions. As a result you have a so-called polygraph chart that is interpreted by specialists to reveal deception.
The problem with lie detector is that it does not detect deception in any direct manner, but rather measures certain physiological responses that are supposed to be stronger if somebody is lying. The polygraph test does not prove to be accurate enough to be relied on. The theoretical basis for polygraph use is weak. There are a lot of different emotions (like fear or anger) and psychological conditions (like illness or pain) that can produce stronger physiological responses, which can be interpreted as an attempt to deceive.
Moreover, the polygraph results depend on how the test is prepared and conducted, i.e. on the specific questions that are asked and the emotional climate of the test. Thus the lie detector use in pre-employment tests is highly problematic, because the results of the test can vary dramatically depending on the above mentioned criteria. The polygraph test proved to be more efficient in law enforcement, where the pool of suspects has a much higher percentage of those who tend to deceive.
The Employee Polygraph Protection Act of 1988, which applies to most private employers, prohibits (with some exceptions) polygraph use for employment purposes. The exceptions include texts conducted to screen federal, state or local government employees; federal government consultants and national security contractors; employees in companies which manufacture controlled substances etc. However, the Act does not prohibit various tests that use other techniques for pre-employment screening and further employment purposes.