TUCoPS :: Privacy :: liedctr.txt

Meet and beat the lie detector

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                      %% Meet and Beat the Lie Detector %%
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                      %%      Stolen from the book      %%
                      %%          BIG SECRETS!          %%
                      %%     by: William Poundstone     %%
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                      %%            Typed By            %%
                      %%   --==**>>THE RELFEX<<**==--   %%
                      %%   [Member: Omnipotent, Inc.]   %%
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                      %%  80-col for Countlegger 8 and  %%
                      %%  various typo. corrections by  %%
                      %%  Count Lazlo Hollifeld-Nibble  %%
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     The polygraph test was invented by William Moulton Marston, who was,
     strangely enough, also the creator of the "Wonder Woman" comic strip
     (under the name Charles Moulton).  The standard polygraph records
     only three distinct vital signs.  A blood-pressure cuff on the upper
     arm measures changes in blood pressure.  Wires attached to the
     fingers measure changes in electrical resistance of the skin due to
     sweating.  Rubber straps around the torso measure the breathing
     rate.  This information is displayed as four squiggles on a moving
     strip of graph paper.

     Whether or not you believe a polygraph provides useful information
     (most psychologists have their doubts), there is a good chance you'll
     be asked to take a polygraph test.  The vast majority of lie-detector
     tests are administered for employee screening--"Have you been using
     the WATS like for personal calls?" and so forth--not for police
     work.  In 'A Tremor In the Blood: Uses and Abuses of the Lie
     Detector' (New York: McGraw-Hill, 1981), polygraph critic David
     Thoreson Lykken estimates that as many as one million polygraph
     examinations are performed on Americans each year.  In criminal cases
     however, even the manifestly innocent may be asked to take a
     polygraph test.  All Yakima County, Washington, rape victims are
     required to take the test; refusal means the case will not be

     At best, all the polygraph can indicate is a heightened emotional
     reaction to a question.  It cannot specify what kind of an emotional
     reaction. Polygraphers try to design question formats so
     guilt-induced nervousness will be the only emotional invoked and so
     the subject's reaction to relevant questions can be compared to
     other, "control" questions.


     This is the question format used in most police investigations.  It
     usually starts with a card trick devised by two pioneer polygraphers,
     John E. Reid and F. E. Inbau.

     The polygrapher hooks the subject to the polygraph and takes out a
     deck of cards.  The polygrapher tells the subject that he must
     "calibrate" the polygraph with a simple test.  He fans the deck and
     asks the subject to select a card.  The subject is told to look at
     the card but not to show it or mention its name.  The polygrapher
     tells the subject to answer "no" to every question asked about the
     card.  "Is it a black card?" the polygrapher asks.  "Is it a high
     card?" and so on.  After each "no" the polygrapher scrutinizes the
     tracings and fiddles with the dials.  If the no answer is incorrect,
     the polygrapher disagrees.  The field is soon narrowed to one
     card--and it is the correct card.

     Needless to say, the polygrapher uses a trick deck.  The point is to
     foster confidence in the machine.  After identifying the card, the
     polygrapher comments that the subject's reactions are particularly
     easy to read and segues into the interrogation.

     Three types of questions are used in a lie-control test.  The entire
     list is read to the subject well in advance of the test.  The start
     of a typical interrogation might run like this:

  1. Is your name Sarah Elkins?
  2. Is Paris the capital of France?
  3. Have you ever failed to report more than $50 of tip, gambling or gift
     income on a single year's tax return?
  4. Is this apple red?
  5. Do you have any idea why the cash reciepts for the last quarter are about
     $22,000 in error?
  6. Is there something important that you did not mention on your job
  7. Have you ever been embezzling from the company?

     The first question is always irrelevant to the matter being
     investigated. It has to be because many subjects get nervous on the
     first question no matter what.  Other irrelevant questions are asked
     throughout the interrogation (questions 2 and 4 in the sample list).
     If the subject gives any thought to these questions, he assumes that
     they are control questions to provide a yardstick for evaluating
     responses to the relevant questions.  Actually, the irrelevant
     questions are there to give the subject's vital signs time to return
     to normal.  They aren't the control questions.

     Questions 5 and 7 in the list above are relevant questions--the only
     questions the examiner is really interested in.  The relevant
     questions are asked in several different wordings during the test.

     Questions 3 and 6 are control questions.  In the pretest discussion
     of the questions, the polygrapher explains that it is helpful to
     throw in a few "general honesty" questions. Whoever committed the
     serious crime, the spiel goes, probably comitted less serious crimes
     in the past.  Hence the inclusion of questions about tax cheating,
     lying on the job applications, stealing as a child, etc.

     The polygrapher affects the attitude that it would be damaging indeed
     to admit any such indiscretions.  Frequently this scares the subject
     into admitting minor crimes.  In that case, the plygrapher frowns and
     agrees to rewrite the question.  Should the subject concede failing
     to report eighty dollars in gambling winnings, question 3 might be
     changes to "Have you ever failed to report more than a hundred
     dollars of tip, gambling, or gift income on a single years's tax
     return?"  If necessary, several of the control questions may be
     reworded before the test--always so that the subject will be able to
     give the "honest" response.

     In reality, the whole point of each working question is to
     manufacture a lie.  It is the secret working premise of polygraphers
     that everyone commits the minor transgressions that are the subject
     of the usual control questions. All the subject's denials on the
     control questions are assumed to be lies.  The polygraph tracings
     during these "lies" establish a base line for interpreting the
     reaction to the relevant questions.

     The reason for rewriting some control questions is so a candid
     subject will no admit to minor crimes on the test.  That would be
     telling the truth, and the polygrapher wants the subject to lie.  The
     control questions are intentionally broad. Even if a question is
     reworded to exclude the confessed instance, it is assumed that any
     denial must be a lie.

     The rationale for the lie-control test goes like this:  The honest
     subject will be worried about the control questions.  He'll know that
     he has committted small transgressions or suspect that he must have,
     even if he can't remember them.  So he'll be afraid that the machine
     will detect his deception on the "general honesty" questions
     (especially in view of its success with the card trick).  That would
     be embarrassing at least, and it might throw suspicion on him for the
     larger crime.  In contrast, the relevant questions should be less
     threating to the honest subject.  He knows he didn't commit the
     crimes they refer to.

     The guilty person, on the other hand, should have far more to fear
     from the relevant questions.  If the machine can detect lying on the
     relevant issue, it matters little that it might also implicate him in
     petty matters.

     By this hypothesis, an innocent person should have greater
     polygraphic response to the control questions than to the relevant
     questions.  The guilty pattern is just the reverse:  greater response
     to the relevant qustions.  This, at any rate, is what polygraphers
     look for when the machine is switched on.


     The relevant-control test is the type used for most employee
     screenings. Thus it is the most common type of examination.  The
     interrogation consists only of irrelevant and relevant questions.  As
     with the lie-control test, the first question and a few others are
     irrelevant.  The relevant questions usually test workplace honesty:
     "Have you ever taken home office supplies for personal use?" "Have
     you ever clocked in for someone else?"

     The premise is that no one will lie about everything.  So if a few of
     the relevant questions produce heightened responses, they are
     presumed to be the questions on which the subject is lying.
     Unfurtunately, there is no ambiguous way of deciding how much
     response is indicates a lie.  Most psychologists agree that the
     relevant-control test is a poor test of deception.

     The Reid/Inbau card trick is eliminated from employee screenings:
     There is too great of a chance of coworkers comparing notes and
     discoverings that everyone picked the ace of spades.


     To the extent that the polygraph works at all, it works because
     people believe it does.  Many criminals confess during polygraph
     examinations.  Many employees are more honest for fear of periodic
     screenings.  But a dummy polygraph that hummed and scribbled
     preprogrammed tracings would be no less effective in these instances.

     David Thoreson Lykken estimates that lie-control polygraph tests are
     about 70 percent accurate.  (Remember, though, that choosing "heads"
     or "tails" of a flipped coin can be accurate 50 percent of the
     time.)  Accuracy of 70 percent is not impressive, but it is high
     enough to talk meaningfully of beating a polygraph test.

     Just by having read this far, you stand a greater chance of beating a
     polygraph test.  You won't be wowed by the card demonstration.  You
     realize that the polygraph's powers are limited.  There are two
     additional techniques for beating the polygraph.  The more obvious is
     to learn how to repress physiologic responses to stressful
     questions.  Some people are good at this one; others are not.  Most
     people can get better by practicing with a polygraph.  Of course,
     this training requires a polygraph, and polygraphs are expensive.

     The opposite approach is to pick out the control questions in the
     pretest discussion and exaggerate reactions to these questions during
     the test.  When the control-question responses are greater than the
     relevant-question responses, the polygrapher must acquit the subject.

     Because breathing is one of the parameters measured, taking a deep
     breath and holding it will record as an abnormal response.  Flexing
     the arm muscles under the cuff distorts the blood-pressure reading.
     But a suspicious polygrapher may spot either ruse.

     A more subtle method is to hide a tack in one shoe.  Stepping on the
     tack during the control questions produces stress reactions with no
     outward signs of fidgeting.  Biting the tounge forcefully also works.
     --William Poundstone

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