Actually it really doesn't matter what you do when taking a polygraph. Despite the overwhelming use by law enforcement, polygraphs vary between 50/50 and about 65/35 in accuracy. Basically they are more dependant on the poly operator rather than the machine itself.
The reason for the dependance by LE is that it is a tool of intimidation rather than an accurate gauge of the truth. Unfortuneately often a truthful answer is interpreted as a "lie" and your fucked anyway. There is a great study on polygraphs that was done by a University in the U.S. a while back where they hired "professional" polygraph operators and had them interview people to tell if they were lying. Each operator was told right before interviewing the subjects whether the people that hired them thought they guy/gal was "lying" or "not lying". Along the lines of "yeah, this is just a formality, we're pretty sure he's lying". In an overwhelming majority of the cases the determination of whether the subject was lying or not came down to the comments before the actual interview.
It's an IDIOTIC technology!!! But of course that doesn't help you when you are forced to take one. Best bet, ALWAYS refuse, even if you are NOT lying. If you have to take one and you are telling the truth, yes you are better off still trying to screw it up into an "inconclusive" result.
Basically if you have an IQ over 80, you should be aware of this and avoiding these stupid machines. Most criminals are bigger idiots than the cops anyway, so it works out in the cops favour.
Apologies to any cops out there (present company excepted).
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