pcslim 2010-07-05:It's impossible to distinguish between anxiety caused by telling a lie and anxiety due to a fear of not being believed when telling the truth. The physiological response measured by the polygraph is identical in both situations and anyone who tells you otherwise is full of crap! The polygraph might be a good interrogation prop, but it doesn't really detect lies. It can intimidate suspects, but that's about it. If when faced with the intimidation of the polygraph a suspect sticks to his/her story, then the suspect is most likely telling the truth. End of story!
AMERICAN PSYCHOLOGICAL ASSOCIATION wrote:The accuracy (i.e., validity) of polygraph testing has long been controversial. An underlying problem is theoretical: There is no evidence that any pattern of physiological reactions is unique to deception. An honest person may be nervous when answering truthfully and a dishonest person may be non-anxious. Also, there are few good studies that validate the ability of polygraph procedures to detect deception. As Dr. Saxe and Israeli psychologist Gershon Ben-Shahar (1999) note, "it may, in fact, be impossible to conduct a proper validity study." In real-world situations, it's very difficult to know what the truth is.
A particular problem is that polygraph research has not separated placebo-like effects (the subject's belief in the efficacy of the procedure) from the actual relationship between deception and their physiological responses. One reason that polygraph tests may appear to be accurate is that subjects who believe that the test works and that they can be detected may confess or will be very anxious when questioned. If this view is correct, the lie detector might be better called a fear detector.
LINK:
http://www.apa.org/research/action/polygraph.aspx