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Polygraphs.  You've seen them in the movies and they always catch the bad guys and exonerate the innocent.  At least in the movies they do.

Polygraphs, or "lie detectors" work by measuring certain physical changes in the person hooked up to it, mainly heart rate and level of perspiration.  The guy running the thing asks a series of relatively innocuous questions, for example, "Have you ever stolen anything in the last 20 years?"  We once borrowed something and have taken far too long to pay it back.  Is that still stealing?  Even the most scrupulously honest of us would find it hard to think back 20 years and not figure there was something we took that maybe we shouldn't have.  It may have been no more than a postage stamp from where we work, but immediately we're a little nervous because we're already under suspicion for something, and we either have to be honest and say "Yes, I stole something", or lie and say "No".

The next question may be more specific.  "Did you steal this money?"  If you didn't, your level of nervousness may go down a bit.  If you did, it may go up.  Unfortunately, the operative word here is "may".  Experienced people have learned to heighten their physical reactions during the more innocuous questions, by biting their tongue, placing a nail in their shoe and stepping down on it, etc.  This way, when the more direct question is asked, even if guilty, their reactions may decrease as they stop biting their tongue or stop stepping down on the nail.

You don't have to be really good at it.  For crying out loud, I once saw Barbara Walters beat the thing!

Of course, most people don't know all the little tricks.  I'm not sure whether Barbara Walters knew the tricks or whether the damned thing was simply wrong.  I just saw her beat it, and the guy giving the test stupidly insisting on its accuracy, even after admitting that she had indeed beat it.

Is a polygraph accurate when used on someone who doesn't know all the little tricks?  Courts and the general public certainly believe in them.  Certainly the spectators on the "Maurey Povich" show trust them implicitly.  Of course, what people believe doesn't really mean anything.  Regardless of what people believe, are polygraphs reliable, or not?

The answer is not only "No", but "Fuck no!"  Research done on polygraph results have revealed that among guilty subjects, the polygraph will pronounce them innocent about 25% of the time.  OK, that's not so bad depending on how you look at it, but here's the truly ugly part.  Among innocent subjects, the polygraph will pronounce them guilty 33% of the time!  The polygraph falsely condemns a full third of innocent people.

The moral here is, if you're guilty, you don't have much to lose by taking a polygraph test.  If you're innocent, stay the fuck away from them!  Chances are one out of 3 that you'll be pronounced guilty and the courts and juries are all too willing to believe it.

Scientists know that these are unacceptable failure statistics even if the court system doesn't.  Scientists are therefore working on instruments that might prove more reliable.  One device measures almost microscopic facial movements.  It's not hard to measure the movements but it is hard to know which movements indicate honest answers and which indicate prevarication.

Another device, an fMRI, (Functional Magnetic Resonance Imaging) shows that certain areas of the brain light up like a Christmas tree when you're lying, and others light up when you're telling the truth, based mainly on stress levels.  Of course, MRI machines are enormous and enormously expensive and not the least bit practical in most cases.  So, scientists are working to develop something a little more portable and a little more affordable.

Now, it might be nice if we always convict the guilty and always exonerate the innocent, but there's something frighteningly Orwellian about machines that could truly read our minds, (or our faces).  Reading some people's minds might make a fascinating read.  For others, it might be more like reading a pamphlet.  Darwin