Don’t trust a lie detector
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.
Then there is this excerpt:
Polygraph testing has generated considerable scientific and public controversy. Most psychologists and other scientists agree that there is little basis for the validity of polygraph tests. Courts, including the United States Supreme Court (cf. U.S. v. Scheffer, 1998 in which Dr.’s Saxe’s research on polygraph fallibility was cited), have repeatedly rejected the use of polygraph evidence because of its inherent unreliability. Nevertheless, polygraph testing continues to be used in non-judicial settings, often to screen personnel, but sometimes to try to assess the veracity of suspects and witnesses, and to monitor criminal offenders on probation. Polygraph tests are also sometimes used by individuals seeking to convince others of their innocence and, in a narrow range of circumstances, by private agencies and corporations…
… For now, although the idea of a lie detector may be comforting, the most practical advice is to remain skeptical about any conclusion wrung from a polygraph.
What does this mean for you? Lie detector results are not admissible in Iowa Courts because they are not reliable. If a lie detector is not good enough for the court, it should not be good enough for you.
Secondly, if offered a lie detector test ask law enforcement this question “If I pass the test do you promise me, in writing, that I will no longer be considered a suspect and you will close your investigation of me?” This promise has never been made and never will be. If law enforcement does not believe that the lie detector is conclusive, you should not either.
Never, ever, take a lie detector test. Period, no exceptions.