Expert Witness Blog
In The Case for Forensic Polygraph Testing in Post-Adjudication Sexual Offender Examination and Management, polygraph expert witness Ken Blackstone writes:
Scientifically based studies have concluded that the carefully administered, “forensic” or single-issue (one relevant issue) polygraph exam, conducted properly and optimally by a qualified examiner, is 89 to 92 percent accurate. It is the most accurate tool available today for determining truth or deception. When any reduction from the disciplined rigors of forensic polygraph examination occurs, the reliability of the results can and must be called into question.
However, in the post-adjudication sexual offender setting, a less rigorous “utility” approach is often taken and the accuracy of polygraph results diminishes for a number of reasons. The training, skills and discipline of the examiner are typically lower; the purpose of the examination may be far different and more exploratory; the questions are more generalized, ambiguous, and sometimes confusing. The accuracy of a 91% accurate exam is now 50-50.
Unfortunately, at the present time, the less accurate “utility” approach is the norm for post-adjudication testing of sexual offenders. As a consequence, treatment providers and community supervisors are impacted by the outcomes of these “utility” examinations, even though the outcomes are unreliable because they are beyond the parameters established by research. Fortunately, the utility test is not a necessity; it is conducted as a matter of economic convenience.
Ken Blackstone is an expert regarding polygraph examinations. He is the author of the book Polygraph, Sex Offenders, and the Court (2011, Emerson Books ISBN 978-061-5506-80-7). www.blackstonepolygraph.com