i just can't see how 'realistically' they can work unless people actually think they do and simply tell the truth because they think they work but then it doesn't cover certain people who 'can tell a lie and prove it'.
Polygraphy has little evidence to support its use. Despite claims of 90% validity by polygraph advocates, the National Research Council has found no evidence of effectiveness. The utility among sex offenders is also poor with insufficient evidence to support accuracy or improved outcomes in this population.Notable cases
Polygraphy has also been faulted for failing to trap known spies such as double-agent Aldrich Ames, who passed two polygraph tests while spying for the Soviet Union. Other spies who passed the polygraph include Karl Koecher, Ana Belen Montes, and Leandro Aragoncillo. However, CIA spy Harold James Nicholson failed his polygraph examinations, which aroused suspicions that led to his eventual arrest. Polygraph examination and background checks failed to detect Nada Nadim Prouty, who was not a spy but was convicted for improperly obtaining US citizenship and using it to obtain a restricted position at the FBI.
The polygraph also failed to catch Gary Ridgway, the "Green River Killer". Another suspect named Melvin Foster allegedly failed a given lie detector test whereas Ridgeway passed. Ridgway passed a polygraph in 1984 and confessed almost 20 years later when confronted with DNA evidence.
Conversely, innocent people have been known to fail polygraph tests. In Wichita, Kansas in 1986, after failing two polygraph tests (one police administered, the other given by an expert that he had hired), Bill Wegerle had to live under a cloud of suspicion of murdering his wife Vicki Wegerle, even though he was neither arrested nor convicted of her death. In March 2004, a letter was sent to The Wichita Eagle reporter Hurst Laviana that contained Vicki's drivers license and what first appeared to be crime scene photographs of her body. The photos had actually been taken by her true murderer, BTK, the serial killer that had plagued the people of Wichita since 1974 and had recently resurfaced in February 2004 after an apparent 25 year period of dormancy (he had actually killed three women between 1985 and 1991, including Wegerle). That effectively cleared Bill Wegerle of the murder of his wife. In 2005 conclusive DNA evidence, including DNA retrieved from under the fingernails of Vicki Wegerle, demonstrated that the BTK Killer was Dennis Rader.
Prolonged polygraph examinations are sometimes used as a tool by which confessions are extracted from a defendant, as in the case of Richard Miller, who was persuaded to confess largely by polygraph results combined with appeals from a religious leader.
In the high-profile disappearance of 7-year-old Danielle van Dam of San Diego in 2002, neighbor David Westerfield became the prime suspect when he failed his polygraph with a greater than 99% probability he was lying. But this claim has been challenged because the examiner kept the space heater on, making Westerfield uncomfortably hot; he constantly adjusted his machine, he said because the readings were too low; and he made a number of subtle changes to the questions he said he was going to ask, even though he said he wouldn’t. The examiner thought Westerfield’s alibi, a meandering weekend trip, was "as crazy as it gets"; he interviewed him for 3 hours, and at the end of the test, accused him of being involved in Danielle’s disappearance. Westerfield attributed his failing the test to his compassion for Danielle's family.In subsequent letters he said that, a couple of days later, they discovered that his test contained false results and they asked him to retake the test, but his attorney, who said it probably meant that the first test wasn’t set up right, wouldn’t allow it.
How to cheat on a polygraph test! I'd imagine lost of this is 'common sense'-if you're up for murder, the questions are going to be relating to it!http://www.wikihow.com/Cheat-a-Polygraph-Test-(Lie-Detector