The Polygraph machine

Is it Science?
The beginning
 The father of the US polygraph machine was Doctor
William Marston
 He designed the first device that measured blood
pressure to determine if someone was being
The Doctor Himself
The Polygraph
 From A polygraph is an instrument that
simultaneously records changes in physiological
processes such as heartbeat, blood pressure,
respiration and electrical resistance.
 Polygraph is used by some employers to screen job
applicants (CIA)
 Extremely hard to come up with empirical results
because no-wrongdoing is expected
 They ask questions they feel may be important in the
future. i.e. past stealing and respect for authority
 Because they use the CQT –often fails
Two myths about the polygraph
 The polygraph provides an objective answer to truth or
 The polygraph is infallible
 Both are wrong!
Two different types of Polygraph
 There are two different types of Polygraph tests that
can be given
 They are:
 The Controlled Question Test (CQT)
 The Guilty Knowledge Test (GKT)
The Controlled Question Test
This type of polygraph exam is the most widely used
Does it have any basis in science? NO!
What happens?
~4 hours
Countermeasures – college students 70%
grounded in theory – – standard procedure –
contamination – objectification –not blinded
The Guilty Knowledge Test
This test is used the least often
Does it have a basis in Science? YES!
How does it work? – doesn’t test lie detection
Controls, grounded in theory – orienting responses –
standard procedure – less contamination
Countermeasures hard to come by
If it is scientific why is it not used more?
Hard to implement: Silence/ large number of questions
Shenanigans – test was designed by scientists – non
scientists who developed the CQT Don’t want to recognize
Empirical Findings of CQT
 First, extremely hard to get data – examiners like to
claim perfection, and it is hard to get exact data.
Out of 250 studies – only 10 were considered to be up
to research standard – and they didn’t even have to do
with testing at a grand scale – just individual instances
Results of the ten:
Correct guilty: 70.6%-98.6%
Correct innocent: 12.5- 94%
False negatives 0-28%
False positives 0-75%
Empirical Findings of GKT
 Testing is still in infancy- but because GKT stands to a
scientific standard – results are highly superior to the
CQT results
 Accuracy rate for guilty – 81%
 Accuracy rate of innocent – 96%
The Polygraph vs the courts
 Frye v. United States 1923
 Established Frye Standard – expert testimony can only
be accepted when the majority of the scientific
community accepts the science.
Daubert v. Merrell Dow Pharmaceuticals 1993
Established the Daubert standard
Judge decides
Testing – falsifiable, known error rate, peer reviewed,
accepted by the scientific community
United States v. Scheffer
Bringing GDT to the courtroom
 the Daubert standard
 falsifiable, known error rate, peer reviewed, accepted
by the scientific community
What can we conclude
 CQT is broken – Stop using it! There is no way to
revive this dead horse
GKT looks incredibly valid – still need some more
research – but it rests on solid ground
However, in this class we are called to be skeptics and
have an open mind, but not too open that our brains
fall out.
Because the evidence supports GDT, I believe there is
something valid about it
This means the polygraph may not have been a
completely worthless device after all
So you all don’t forget – laundry list
of problems with the CQT
 No objectification – Also, can’t compare results
 Only 15 minutes with actual device
 Easy to beat – agree to questions beforehand
 Because of post-test interview – no legitimate amount
of records
 Baseless theory – changes in physiological >>>
 Technology has stayed put
Dr. Travis Patterson
 “Numerous scientific papers by knowledgeable
individuals have been presented in affirmation
and rejection as to the absolute reliability
regarding any and all of these procedures”
 : “various procedures – finger prints, blood
analysis, psychological approaches, psychometer
procedures, psychiatry, etc – have been adopted,
and accepted, by the courts in determining an
expedient conclusion” (Patterson).
 Questions?

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