Wednesday, October 05, 2011

All about lie detectors...

While Canadian crime investigators use the polygraph as an investigative tool, our courts ban polygraph results from being presented as evidence because of their unreliability.  Just how accurate are polygraphs and can they be used in crime prevention? 

Polygraph expert, Ken Blackstone, gives us the latest low down on polygraphs and their use south of our border.

The Case for Forensic Polygraph Testing in Post-Adjudication Sexual Offender Examination and Management

By Ken Blackstone

In 1973, in the Multnomah County Circuit of Oregon, Judge John C. Beatty, Jr. was the first to order the use of the polygraph in the management of convicted sexual offenders. Today, almost 40 years later, the number of registered sex offenders in the US and its territories exceeds half a million and they are all under some form of management. The post adjudication polygraph is used by the responsible State and Federal agencies in three common circumstances: in prisons during the incarceration of convicted sex offenders; in the community during subsequent probation and parole; and during the civil commitment of sexually dangerous persons.  

The Problem

Polygraph examination is a catch-all term used to describe the use of the polygraph instrument, either as a forensic tool to determine the veracity of a statement or as a utility tool to generate statements and disclosures. While these two approaches are superficially similar their foundations are not.  

Law enforcement agencies use polygraph to support investigation of criminal matters and attorneys use the polygraph both for establishing direction in their cases and to present as evidence in an upcoming proceeding.  Whether the polygraph examiner conducts a forensic examination that is reliable or a utility examination that is undependable is often unknown to the agencies and attorneys involved.
In a pre-adjudication setting a suspect or person of interest may be asked to take a polygraph examination as a means of assessing his or her denials about being knowledgeable, involved or even responsible for the alleged crime.  A witness or informant may be asked to submit to a polygraph for the purpose of assessing the accuracy or truth of information he or she has provided.  Although it is barred in some states, in some cases, an alleged victim of a crime may be asked to take a polygraph test to determine the accuracy or truth of testimony to either support the conviction of a guilty person or prevent the wrongful prosecution of an innocent person.  Thus, polygraph examinations are a very serious matter that has great importance and impact on the tested individuals and the matters to which they offer evidence.   These situations are all alike in that there is an “issue at hand” and they are truly voluntary.

In a post-adjudication setting a convicted or committed offender is expected to take periodic polygraph examinations to encourage candor and discourage any lapse or relapse during treatment and supervision.  The use of the polygraph in the evaluation and management of convicted and committed sex offenders is of great interest; treatment providers will often agree that the polygraph is the only existing tool for measuring behavior and supervising officers see the polygraph as a way of keeping offenders accountable. A periodic post-adjudication polygraph examination in the community can be used to assess a variety of issues that may include precursors to a reoccurrence and whether the convicted person should be considered for early release of parole or a relaxation of probation controls.     These situations are similar in these examinations will seldom address a specific “issue at hand” and while they are an option the only other option is prison.

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, utility testing 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.

Proposed Solution

Forensic polygraph examination has safeguards which keep its error-rate below 10 per cent.  This type of polygraph testing is frequently used in the legal, intelligence and investigative communities.  Its popularity in the Federal and State agencies arena is encouraged by the high caliber of training and supervision provided its examiners. Similar standards and training need to be developed and deployed in the area of post-adjudication assessment and management of sexual offenders.

Utility tests, such as the ones most currently popular in sex offender management programs, actually invite errors (false positives and false negatives). A “false positive” can result in a waste of professional resources and it can unfairly hamper the otherwise honest sex offender who is trying to rebuild his life.  A “false negative” can allow recidivism that could have been stopped before anything happened*. Here are some examples where forensic polygraph examination may have helped prevent tragic crimes from occurring:

* Phillip Garrido was a registered sex offender on Federal and State parole for rape when he abducted then 11-year-old Jaycee Dugard and while he held her captive for the next 18 years.  He was excluded from required polygraph.

*John Couey was a registered sex offender in Florida and was on state probation when he abducted, raped, and murdered then 9-year-old Jessica Lunsford.  His probation supervision failed and he was excluded from polygraph surveillance.  Jessica’s body was discovered as a result of a polygraph examination.

Examples such as Garrido and Couey represent statistical outliers; however they underscore the need for a disciplined approach that requires forensic testing methods and standards. 


Post-adjudication testing of convicted sex offenders is a different arena than pre-adjudication testing; however, it does not require a “reinvention of the wheel”.  The parameters of forensic testing already exist.  The responsible agencies, instead of ignoring these disciplines, should incorporate them into their existing discipline. This, among other things, will improve the quality of post-adjudication polygraph examiners and their work product by: 

1.      Providing specialized forensic level training for these post-adjudication polygraph examiners

2.      Establishing standards for the conduct of professionals in post-adjudication polygraph testing

3.      Setting requirements for the deployment of diagnostic single-issue testing during examinations

4.      Providing supervision in the form of quality control and classroom review of examinations.

5.      Providing training for non-examiner treatment providers and other professionals who are involved in sex offender management.

About the Author


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). Since 1979 he has been involved in more than 23,000 polygraph examinations as an examiner, consultant, and expert witness. He has conducted more than 15,000 examinations and consulted on a thousand more, including several high profile cases (including the Jon Benet Ramsey case and the Troy Davis case).  He has written numerous peer-reviewed articles on polygraph and forensic interviewing. The majority of his career has focused on sexual offense cases and the examination of convicted and/or committed sexual offenders. He lives in Stone Mountain, Georgia.  
Author, Ken Blacksone's, website

No comments: