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Study Testing the Validity of Truster-Pro Voice Analysis Technology in a Criminal Field Context
By
John Joseph Palmatier - Ph.D.
Subjects
scheduled for criminal polygraph examinations conducted by a large
Midwest state police agency, for crimes ranging from larceny to
murder, gave permission to record their vocal responses to questions
asked about the issue at examination. These recordings were used
here to test the predictive validity of a new voice analysis
technology created in Israel by Trustech Inc. Two polygraph
examiners, one a trained voice stress analyst, created the voice
recordings using digital audio tape (DAT) decks prior to collecting
the physiological data and conducting the field polygraph
examinations. The voice data of 100 subjects was selected from 296
consecutive polygraph examinations. Selection was based upon the
existence of ground truth, i.e., the presence of specific details in
the subject's (or another person's) subsequent confession, 25
truthful control subjects, 50 deceptive and 25 truthful subjects,
were selected from the field polygraph examinations administered by
the two polygraph examiners. Either the examinee or another person
confessing to the crime at issue confirmed examinee status.
A trained voice
analyst in Israel, Dr. Albert de Vries analyzed the voice recordings
using the Trustech software and rendered decisions regarding each
subject's status. Results show that when examiner training was not
considered, and only a truthful/deceptive decision allowed, the
voice analyst achieved an overall accuracy rate of 78% for truthful
subjects and 61% for deceptive subjects (P2(1, N = 99) = 15.693,
D<.000). These results were contrasted with those of six trained
polygraph examiners who blind scored the exam's physiological data.
A US government trained examiner achieved the greatest degree of
accuracy. And in this context achieved an overall accuracy rate of
51% for truthful subjects and 92% for deceptive subjects (P2(1, N =
90) = 20.627, D<.000). Although the ability to detect deceptive
subjects appeared impressive, it was achieved by labeling 49% of the
truthful subjects as deceptive. A practice that may be acceptable in
a security context, may have serious policy implications in many
other settings.
When the voice
analyst and the polygraph examiners were asked to render
truthful/inconclusive/deceptive opinions, the data analysis showed
that excluding inconclusive decisions, the voice analyst achieved an
accuracy rate of 89% for truthful subjects and 64% for deceptive
subjects (P2(1, N = 56) = 17.143, D<.000). The government
polygraph examiner achieved an accuracy rate of 83% for truthful
subjects and 76% for deceptive subjects (P2(1, N = 77) = 23.326,
D<.000).
Further analysis showed that examiner training was an important and
contributing factor. When the voice analyst rendered decisions on
those examinations administered by the polygraph examiner with no
voice training, there was no significant discrimination between
truthful and deceptive subjects. The accuracy of the voice analyst's
decisions for those subjects tested by the examiner with voice
stress analysis training however, were notably different. When the
voice analyst was asked to render only a truthful/deceptive opinion
his accuracy rate was 81% for truthful subjects and 71% for
deceptive subjects (P2(1, N = 77) = 20.715, D<.000). When the
voice analyst was asked to render a truthful, inconclusive or
deceptive opinion, and the inconclusive decisions were excluded, the
analyst achieved an accuracy rate of 89% for truthful subjects and
78% for deceptive subjects (P2(1, N = 77) = 19.684, D<.000. For
the same sample, the polygraph examiner making a truthful/deceptive
opinion achieved a 49% accuracy rate for truthful decisions and
again, a 92% rate of accuracy for deceptives (P2(1, N = 69) =
13.911, D<.000). Excluding inconclusive decisions, in a
truthful/inconclusive/deceptive decision making context, the
polygraph examiner achieved a 56% rate of accuracy for truthful
subjects and 88% for deceptive subjects (P2(1, N = 58) = 12.796,
D<.000).
The voice
analyst's decisions regarding the status of the 25 control subjects
were notable. When asked to render only a truthful/deceptive opinion
the voice analyst accurately identified 84% of the truthful control
subjects. When asked to render a truthful, inconclusive or deceptive
opinion, and the inconclusive decisions were excluded; the voice
analyst then achieved a 100% rate of accuracy. In a
truthful/deceptive context, the polygraph examiner making decisions
on 20 of the 25 control subjects, accurately identified 70% of the
control subjects status. When the polygraph examiner rendered a
truthful, inconclusive or deceptive opinion, and the inconclusive
decisions were excluded; a 79% rate of accuracy was achieved.
These
results are comparable to those found in some field validity studies
that have examined the psycho-physiological detection of deception (PDD).
Moreover, they suggest, at least in a criminal interrogation
context, that the Trustech technology may provide some benefits not
realized through the use of the polygraph, that is, the accurate
classification of subjects who are in fact truthful. Together, these
results and the versatility of the Trustech voice analysis software,
would strongly suggest that additional research is needed to explore
this new and promising technology in multiple settings and to
investigate the effects that training, and the use of various
testing procedures may have in different contexts.
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