This test relies on the liar have an emotional reaction to the act of lying. The more the reaction the greater the indication of lying as the polygraph picks up the emotional tension. This statement describes what happens to some people when they lie
Thus the lying transaction could be diagramed as such
The lying transaction.
The Parent ego state of the individual tells the Child ego state that it is wrong to lie. The Child ego state feels guilt in response to that parental directive if they choose to lie. The Child ego state also experiences another emotion, that of fear of getting caught.
For most people this applies. However there are a group where this does not apply and that is with the anti social personality. As a consequence one of the personality traits of this personality is that they lie more than most. Another feature of the anti social personality is they do not feel fear like the average person. They fail to comprehend the long term consequences of what they are doing and hence feel less anxiety. A teenager is also like this. They will take risks because they do not perceive the potential danger and thus do not feel the fear in the first place.
I didn't do it!
So the polygraph is less effective with the anti social personality and to a lesser extent the average teenager. The anti social will have less of a fear reaction and hence it wont show up on a polygraph test. They also have poor moral development in their Parent ego state and hence do not have a moral directive against lying. Hence they do not feel guilt like the average person and again this make the polygraph test ineffective.
I would also add one other possible flaw with the poly graph and one sees this particularly with drug uses. In the drug subculture lying is endemic. People often lie to conceal the activities they are doing. As a result lying can become habitual like any behaviour can. When working with them you will find them lying at times when there is no reason to. They are simply doing it out of habit. I would suggest that such a person who lies habitually would also have much less of a fear and guilt reaction in a polygraph test.