They do work. Their purpose is intimidation. They’re not truth machines, they’re pressure cookers.

They have only filter out the morons, though.

Exactly, the whole point is to put someone into an interrogation scenario for hours or days, where you control whether nor not they "passed". Unfortunately, it probably has zero effect on psychopaths.

There's an old interview on C-SPAN's BookTV with a CIA polygrapher. He seems to genuinely believe in the validity of the polygraph, but watching the interview, I was convinced that the only value comes from intimidation and stress.

(all-caps bad transcription)

> THE ESSENCE OF A POLYGRAPH TEST IS IF YOU HAVE SOMETHING TO LOSE BY FAILING A POLYGRAPH TEST IF YOU WILL, OR SOMETHING TO GAIN BY PASSING IT, THAT IS WHAT MAKES THE POLYGRAPH EFFECTIVE. WITHOUT THE FEAR OF DETECTION IT IN A SIMPLE WAY AS I CAN PUT IT THAT IS WHAT MAKES IT WORK. YOU HAVE TO BE AFRAID. IF YOU HAVE NOTHING TO LOSE BY TAKING THE POLYGRAPH TEST THAN THE PRESSURE IS NOT ON YOU. BUT AS I SAID THAT IS WHAT MAKES YOU WORK. IT HAS TO BE PROTECTION MORE THAN GILTS. NOW YOU MAY FEEL GUILTY, BUT FEAR OF DETECTION IS THE OVERRIDING CONCERN IN IN A POLYGRAPH TEST

https://www.c-span.org/program/book-tv/gatekeeper/180053