Polygraph Testing

Polygraph tests, more commonly known as lie detector tests, have been placed in a category of pseudoscience although some still think they have a scientific basis. In 1988, the US government passed the Employee Polygraph Protection Act, which banned the use of the polygraph testing for pre-employment purposes. The test consists of two main parts; the subject is first asked a few "control questions" followed by questions that have to do with the purpose of the test. The control questions are set in place to create emotional discomfort. 

The biggest issue with these tests are how they are measured. The test has a physiological recorder that measures blood pressure/heart rate, respiration and skin conductivity. The use of these measurements makes an invalid assumption that there is a standard correlation between the physiological changes and deception. A nervous person may be innocent but afraid to answer the questions while a guilty person could be non-anxious. Another issue with lie detector tests stems from how the amount of physiological change leads to deception. Does it have to be an overwhelming difference or a slight difference? Polygraph tests have been proven to get guilty people to confess but there is a 50:50 chance that is will falsely identify an honest person as guilty.

http://www.science20.com/gerhard_adam/pseudoscience_lie_detectors-93551

http://www.nolo.com/legal-encyclopedia/lie-detector-tests-tell-truth-29637.html