how polygraphers can detect countermeasures

[Bill Crider]

We've seen a lot of posts lately with polygrpahers saying "we can detect CMs", "no you cant" and so on. I think it boils down to this.

The test measures 3 physiolgical responses. GSR,  pulse and diaphram contraction/expansion as part of breathing. I am quite certain that polygraphers can detect SOME countermeasures such as the guy that holds his breath for a full second or whose GSR goes off the charts because he's giving his @ss a white knukle contraction. or whatever. However, it is, I am certain, virtually impossible to detect well practiced countermeasures. Why do i say this? The test ASSUMES deception by measuring slight changes in these readings consistent with what happens when people do in fact lie. The Polygraph community commits what is known in the world of statistics as a type I error. Just because most liars have physiological changes, it does not follow that people who exhibit these changes are lying. Thus, when someone can alter their reactions in a way that is the same magnitude of change as what might occur if they were lying,  it is impossible to tell what is causing the change.

Im sure the polygraphers will disagree. in that case, please respond by telling me how you know a 20 BPM change in pulse for example is caused by nervousness related to lying as opposed to being a controlled reaction by a skilled examinee. or for that matter as being caused by nervousness for reasons other than lying.

as a ps-i know that only a certain section of the reponse time is the scorable region, and perhaps people who use CMs either do them too strong or at the wrong time. for instance, in the FBI polygrpah, the corable region is the period of time RIGHT AFTER the question is asked and for maybe 5 seconds after the answer is given. I suspect that many people who use CMs wait until after the answer to apply and this could be a factor that you use to determine this. My point is that well trained CM users--it is very difficcult to detect. Studies have shown this to be true. (Charles Honts)