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During the chart collection phase, the examiner will administer and
collect data on several charts. He may allow the subject to
explain any responses or reactions to certain questions. After
that, the results are analyzed.
One of the early innovations in technique was known as "The
Control Question Test." As the examiner gathers
biographical information, he impresses upon the person that honesty
must be established throughout the procedure. Some examiners
used a bit of intimidation to get their point across.
For example, one approach was the "stim test," in which a
subject was shown several playing cards. He was to take one,
look at it, and then place it back in the deck. The examiner,
who had not been told what the card was, shuffled the cards and then
told the subject to say 'no' to each question about the cards he was
shown, including the card that he drew from the deck. That
meant that one of his responses would be a lie. Then the
examiner picked the card that the subject drew to give the
impression that the machine is infallible. In fact, the
examiner knew which card the subject had picked. Thus, deception was
employed by some to strongly persuade a subject to tell the truth.
(It should be noted that not all polygraph examiners used or even
approved of this technique.)
Then, as with the R/I test, the examiner asked two types of
questions: "Relevant" questions were related to the
crime and "control" questions were based on common
misdeeds such as petty theft or betrayal, and were calculated to
inspire an emotional reaction from the subject. The assumption
was that subjects would deny doing them, but was more likely than
not to be lying. Thus, their "deception response"
could be measured. When lying, then, innocent subjects would
be more aroused by the control questions, while guilty subjects
would react most strongly to the crime-relevant questions.
After the data is in, the charts get interpreted.
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| The polygraph drawing lines (AP) |
The polygraph today is a compact device small enough to be portable.
Rubber tubes are placed on the examinee's chest and abdomen, as well
as a blood pressure cuff on the arm and small metal plates attached
to the fingers. The primary mechanism uses a moving paper
feeder and styluses that record the simultaneous input from three
involuntary physiological responses: galvanic skin response,
relative blood pressure, and respiration. Some instruments add
peripheral blood flow (from placing a plethysmograph on the finger).
The moment when a question is asked is marked on the paper, just
before the response gets recorded.
The data are then interpreted through
a numerical scoring system, according to deviations from a baseline
that occur when the subject shows a physiological response to a
question. The examiner interprets the data according to the
magnitude of the deviation and may also use his observations of the
subject under interrogation. He then concludes one of three
things from the score:
- the subject was truthful
- the subject was deceptive
- the results were inconclusive
In 1981, psychologist and prominent polygraph critic, David Lykken,
developed yet another test. He called it "The Guilty
Knowledge Test." He felt that the goal of using a
polygraph should be centered on detecting the presence of covert
guilty knowledge of a crime in the suspect's mind, because subjects
are aroused by a meaningful stimulus that has some association with
the crime, which he called the "orienting response."
As such, the procedure involved a full
awareness of the facts that had been gathered by investigators,
which would be known only to them, the victim(s) and the
perpetrator. For example, in the case of Charles Schmid of
Tucson, who in 1965 had killed three girls and buried them in the
desert, had he been thus interrogated with Lykken's method,
questions might include:
- What were they wearing when they died?
In what part of the desert were they buried?
How were they killed?
What was used to tie them?
Had anyone assisted him?
Had he told someone about what he'd done?
Was anything buried with them?
Had he taken anything off of one of them?
The examiner uses this information to
create a series of multiple-choice questions, which would be
presented to the suspect, with a direction to respond to each
choice. Supposedly, a guilty person reacts to recognizing
certain details, especially if he believes that he is the only one
who knows something. For example, Schmid might not have
realized that a friend had turned him in, and something that he had
said in confidence to that friend—which would be revealed during
questioning—ought to elicit a strong response.
The main problem with this test is
that some offenders pay little attention to the details, so they
might not even recognize significant things about the crime.
It can also be the case that a person has "guilty
knowledge" because he was told about the crime, not because he
participated.
Regardless of the method used, the
main issue centers on just how accurate the polygraph really is.
The American Polygraph Association states that a survey of over
eighty studies indicates that the polygraph has a high degree of
validity, but accuracy depends on having a properly trained
examiner, a good instrument, and on administering it using an
accepted testing procedure and scoring system. That means
there are a lot of factors to coordinate.
Critics of the polygraph are quick to point out significant problems
with its reliability, so let's see what they have to say.
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