The Skeptics Dictionary (http://skepdic.com/polygrap.html) has a good short essay on why polygraphs are a load of pseudoscientific rubbish.
In short “The reason the polygraph is not a lie detector is because what it measures–changes in heartbeat, blood pressure, and respiration–can be caused by many things.” including “having to go to the bathroom”. Further there is significant potential for abuse through invasion of personal lives and intimidation.
I have an anecdotal incident: Frontier Airlines, Denver, circa 1980, used ticket stock was reported as missing. The agent who handled used tickets swore that he counted them, put them in their proper envelopes and deposited them in a trunk located on the floor directly behind his desk. At a certain time each day, someone retrieved the tickets and forwarded them to Accounting.
The employee was fired after taking a lie detector test which he failed. About six months later someone noticed that one Vietnamese janitor faithfully opened the trunk and put all its contents into his trash bin. He said that he’d done so since he started working, that no one had told him otherwise. The employee was reinstated with back pay. The Airline Employees Union directed all employees to never submit to lie detector tests.
At the same time I read about other false results from lie detector tests; unfortunately it was so long ago that I can’t provide cites. Two instances stand out: a suspect who couldn’t answer a question about a previous arrest. It turned out that the suspect was a juvenile offender who had his record erased at age eighteen because of his subsequent good behavior. As far as the law was concerned, he didn’t have a record. As far as he was concerned, he did. The other case was about a man who was questioned about whether or not he had been married before. He answered ‘no’ and failed. Seemed he’d been married but it was annulled. As a fundamental Catholic, he believed marriage was forever.
I saw that in a very old movie.
I am ashamed to admit that I was unfamiliar with the
expression old saw. By teaching it to me, it is you who
have lessened my ignorance. I apologize and sit corrected.