They are debunked, but they're still intimidating enough to be useful on a lot of people. I have friends who claim to have 'faked out' their poly, and friends who claim they cracked under the pressure and tried to admit everything wrong they'd ever done in their life (not that the examiner cares about throwing a frog at your sister when you were 5). On balance, it's useful for weeding out a certain percentage of people.
That doesn't stop the NSA from doing them. I applied to work for the NSA as a mathematician in 2007-8 and went through two separate trips to Fort Meade and two separate polygraphs.
It's not about collecting or verifying information.
The goal of the exercise is to make you fearful, intimidated, and compliant, and to reinforce the government's dominance over you. The polygraph is just a prop. The examiner is the one really measuring you. Even if your saint's halo is still slightly visible at noon on a sunny day, you will always be given the impression that you barely passed.
So it hardly matters that a polygraph is pseudoscience, because the placebo effect is real. If you think you're being objectively measured by a machine, instead of subjectively judged by a man, that makes his job simpler.
Otherwise, it's Iocaine Powder.
(I can neither confirm nor deny whether I have any actual experience with polygraph testing, or whether I know anyone who does.)
I remember seeing a U.S. government counterintelligence film (maybe linked from HN?) meant to discourage people, especially exchange students, from being recruited as assets of Chinese spy agencies. It was based on a true story in which an American was recruited and then applied for a clearance at the instigation of his foreign contacts. In the film, he was caught as a result of failing a polygraph: when uncomfortable questions arise during the examination, he asks to discontinue it and withdraw his application, and they don't let him get away with that; they end up prosecuting him and he pleads guilty to espionage charges.
I couldn't help thinking that the polygraph might have worked in that situation mainly because he believed it would!
That's somewhat of an insider joke about security clearances. (Though I can still neither confirm nor deny that I am an insider, or that I understand why the joke I just told may or may not be funny.)
Pseudoanonymous people posting on the Internet can't be trusted anyway, right?
