* Originally by Sheppard Gordon * Originally to All * Originally dated 28 Aug 1993, 10:24
* Originally by Sheppard Gordon
* Originally to All
* Originally dated 28 Aug 1993, 10:24
[Beating a polygraph machine is easy. This text file suggests some
simplistic strategies. No one should consider individuals who pass
a lie detector as having proven their innocence. On the other hand,
individuals caught trying to deceive a polygraph machine probably
should be considered guilty until proven innocent.]
How to Beat A lie Detector
By The Reflex
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
records three distinct vital signs. A blood pressure. Wires attached
to the fingures 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 paper.
Whether or not you beleive 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 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'
(NY : 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 prosecuted.
At best, all the polygraph can indicate is a heightened emotional
reaction to a question. It cannot specify what kind of emotional
reaction. Polygraphers try to design question formats so guilt
induced nervousness will be the only emotion invoked and so the
subject's reaction to relavent questions can be compared to other,
THE LIE DETECTOR TEST
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 then tells the subject that he must
"Calibrate" the polygraph with a simple test. He fans out 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 tracing
and fiddles with the dials. 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 detector 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 years tax return?
4. Is this apple red?
5. Do you have any idea why the cash receipts for the last quarter
are about $22,000 in error?
6. Is there something important that you did not mention on your
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 subject 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 questions to provide a yardstick for
evaluation responses to the relevant questions. Actually, the
irrevelant questions are there to give the subjects vital sign time
to return to normal. They aren't the control questions.
Question 5 and 7 in the list above are relevant question -- the only
questions the examiner is really interested in. The relevant
questions are asked in several different wordings during the test.
Question 3 and 6 ARE control questions. In the pretest discusion of
the questions, the polygrapher explains that it is helpful to throw
in a few "general honesty" questions. Whoever committed the serious
crime, as the spiel goes, probably committed 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 any such indescretions. Frequently this scares the subject into
admitting minor crimes. In that case, the polygrapher frowns and
agrees to rewrite the question. Should the subject concede failing to
report eighty dollars in gambling winnings, question 3 might be
changed to "Have you ever failed to report more than a hundred
dollars of tip, gambling, or gift income on a single tax return?" If
necessary, several of the control questions mey be reworded before
the test-- always so that the subject will be able to give "Honest"
In reality the whole point of each working question is to manufacture
a lie. It is the secret working premise of polygraphers that every-
one 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
The same reason for rewriting some control questions is so a candid
subject will not admit to a 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 taht 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 committed 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
threatening 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 matter little that it might also implicate him in
By this hypothesis an innocent person should have greater polygraphic
response to the control questions than the relevant questions. The
guilty pattern is just the reverse: greater response to the relevant
questions. This at any rate, is what polygraphers look for when the
machine is switched on.
THE RELEVANT CONTROL TEST
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
honsety: "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 questions on which the subject is lying. Unfortunately
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
discovering that everyone picked the ace of spades.
HOW TO BEAT THE LIE DETECTOR
To the extentthat the polygraph works at all, it works because people
believe it does. Many criminals confess during polygraph examinations
But a dummy polygraph that hummed and scribbled preprogrammed
tracings would be no less 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 precent 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 at this one, others aren't. Most people can get
better by practicing with a polygraph. Of course, this training
requires a polygraph, and they're expensive.
The opposite approach is to pick out the control questions in the
pretest discussion and exxagerate 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 blod pressure reading.
But a suspicious polygrapher may spot wither 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 outword signs of fidgeting. Biting the tongue forcefully also
works. Can you imagine the polygrapher's response to the "Is this
apple red?" question when you say "red" and the machine starts
going crazy? He'd shit his pants!
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E-Mail Fredric L. Rice / The Skeptic Tank