Why giving polygraph tests to sex offenders is a terrible idea
By Chris French
The Guardian - August 10 2012
Polygraphs are notoriously unreliable and easy to fool, and sooner or later sex offenders will discover the truth about them
It was recently announced
that the government is keen to introduce mandatory polygraph testing
for rapists and other serious sex offenders when they are released from
prison, in the hope that this will reduce re-offending rates and thus
protect the public.
A pilot study
has been carried out in the East and West Midlands suggesting that the
routine use of such testing would lead to offenders being more honest
with their offender managers. Offenders undergoing polygraph testing
made twice as many "clinically significant disclosures" as a control
sample. CSDs were defined as "new information that the offender
discloses, which leads to a change in how they are managed, supervised,
or risk assessed, or to a change in the treatment intervention that they
receive." Examples included disclosures relating to increased access to
children or contact with other known sex offenders.
It seems,
however, that these encouraging results were based not upon the ability
of the test to detect when offenders are lying, but instead upon the
offenders' belief that the test was capable of doing so. This raises
serious issues regarding the wisdom of rolling out such a scheme on a
mandatory basis across England and Wales.
Polygraphs are often
wrongly referred to as "lie detectors". In fact, all that polygraphs do
is measure various psychophysiological indices of arousal, such as skin
conductance, blood pressure and respiration. It is assumed that most of
us, when we lie, become more emotionally aroused. Polygraph operators
claim to be able to detect such tell-tale signs of arousal and use them
to determine whether a person is telling the truth or lying.
There
are several different techniques used in this context, but most rely
upon the notion that liars will be more aroused when answering
"relevant" questions compared with when they answer "control" questions,
due to their fear that they will be detected.
Studies have shown
that in general polygraph tests correctly identify about 85% of guilty
individuals. This may appear to be impressive at first sight but it is
necessary to take into account the proportion of innocent individuals
who are wrongly classified as guilty. According to a report by the British Psychological Society in 2004, reviews suggest that between 12% and 47% of innocent individuals are also classified as lying.
Innocent
people may be more aroused by the relevant questions than the control
questions for a variety reasons. For example, suppose the suspect did
not commit the crime in question but was engaged in some activity at the
time that, although perfectly legal, he or she was ashamed of.
Alternatively, it may simply be that the suspect is terrified that he or
she will not be believed despite their innocence.
It is clear
from the results of the pilot study that it was the sex offenders'
belief that the polygraph would detect deception that led to the
increase in disclosures. Not only did most of the these disclosures take
place during the polygraph session as opposed to during routine
supervision, but they actually took place during the pre-polygraph
interview before the test itself was carried out.
Indeed, a previous experiment by the lead author of this pilot study, Theresa Gannon,
clearly showed similar effects among a group of child molesters. Those
who were connected up to a convincing, albeit fake, "lie detector" gave
more honest responses on a questionnaire than those who were not
connected.
It is clear that offenders only have to spend five
minutes on Google to realise that experts generally agree that polygraph
testing is in fact not a reliable technique for detecting deception. If
such testing becomes mandatory, it is inevitable that this truth about
polygraphs will become widely known among offenders. From then on, any
effect that unfounded belief in the effectiveness of the technique had
in terms of increasing disclosures is likely to disappear.
To make
matters worse, techniques exist to beat the test. Once the underlying
rationale of the test is understood, steps can be taken to either
augment the psychophysiological response to control questions (eg via
self-induced physical or mental pain) or else reduce the response to
relevant questions (eg using mental training, such as meditation).
Vaughan Bell described the case of Floyd "Buzz" Fay,
who was wrongly convicted of murder on the basis of polygraph testing.
During his time in prison, Buzz found out as much as he could about the
polygraph and used his knowledge to train other prisoners to beat the
test. After a mere 15 minutes of instruction, 23 of 27 inmates were able
to beat the test. It is highly likely that a sex offender who was
motivated to beat the test and thus give the impression of being low
risk would easily be able to do so.
There is another reason to be
cautious about the results of this pilot testing, one that was noted by
the authors themselves. In their words, "It is possible that polygraph
offender managers may have felt more motivated or 'expected' to provide
large numbers of CSDs compared to comparison offender managers."
By its nature, the design of this study could not be double- or even single-blind
and it is highly likely that this would have had an effect on the
results. In other words, the managers' body language and interpretation
of offenders' responses could have been subconsciously skewed.
The
authors of the report estimated that polygraph testing would cost
between £400 and £937.30 for each additional disclosure that resulted.
Obviously, any intervention that might reduce offending is worthy of
serious consideration. But we should be cautious about implementing an
intervention that might only be effective for the short time it would
take before the truth about polygraphs becomes common knowledge among
offenders.
Perhaps even more worrying is the prospect that a
motivated high-risk offender could probably beat the polygraph from the
outset after just a little bit of background research.
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