Questionable FBI PracticesLaw enforcement engages in a lot of questionable practices that are not based on scientific thinking. Here's an excerpt from a very interesting article about such practices.
Does this sound familiar? The same problem exists with the polygraph, a favorite tool of the FBI and other law enforcement agencies. The polygraph measures such things as heartbeat, blood pressure, and respiration. The polygraph is not a lie detector because changes in heartbeat, blood pressure, and respiration can be caused by many things. Nervousness, anger, sadness, embarrassment, and fear can all be causal factors in altering one's heart rate, blood pressure, or respiration rate. Having to go to the bathroom can also be causative. There are also a number of medical conditions such as colds, headaches, constipation, or neurological and muscular problems that can cause the physiological changes measured by the polygraph. The claim that an expert can tell when the changes are due to a lie and when they are due to other factors has never been proven. Why do so many people, in and out of law enforcement, believe the polygraph is a lie detector? For the same reason that many believe that profiling is accurate, that their daily horoscope is right on, that their tarot card reader is clairvoyant, that John Edward gets messages from the dead, that graphology can reveal the true character of a person, and that Rush Limbaugh is a national treasure: the belief is rooted in cold reading and subjective validation, and grows in soil fertilized with a lot of confirmation bias and communal reinforcement.
LINK:
http://www.skepdic.com/refuge/funk58.html