@camlok,
They are not accepted in court because a polygraph can only tell that you are:
- very nervous about something; or
- hiding something
It doesn't mean you are lying about the answer:
- the nerves may relate to the way in which the question is asked by the interviewer
- in very serious cases (eg murder), nerves may relate to the seriousness of the question (the person wondering if they sound believable or not, even when telling the truth)
- the nerves may relate to the persons worry about the believability of their story, even though it's true
- the nerves may be related to something else, related to the question, that you are trying to hide, but isn't part of the investigation (eg. an affair, or some severely embarrassing moment you don't want anyone knowing)
- some people suffer anxiety as an everyday experience, and their anxiety may increase of it's own accord as the interview progresses
Given all that, I'd be surprised if any court put weight in such. Probably useful for an intelligence agency, where they know who they are working with, are familiar with the persons character traits, and the intelligence agency doesn't have to prove anything relating to their employee beyond reasonable doubt.