annettek:

squaccy:

If the polygraph is only measuring skin conduction and pulse, then the reliability is 90% ish. If the polygraph incorporates all those PLUS brain waves, it is then harder to fool. We did test a polygraph which only had skin conduction and pulse and out of 10 people testes only 1 managed to fool us.

There's some contention over what is actually being measured.

Skin conduction and pulse indicate nervousness, not truth/lie.

Skin conduction and pulse indicate nervousness, not truth/lie: no sorry, skin conduction and pulse indicate nervousness when faced with the possibility of trying to hide a lie. It comes from the fight or flight mechanism. you can't measure truth or lies because they are not actual measurable variables. So you can only measure nervousness  while trying to deceive the person. To back up my point, the experiment we did was that we gave the participant a number (the teacher couldnt see it) and he asked the participant a set of predetermined sequences of numbers and the participant could only say no. then we'd look at the skin conduction and pulse and in 18 out 20 cases it was obvious when they were lying as their skin conduction and pulse went off the charts.