What is a Polygraph (lie Detector)?

By: Marvin Badler

What is a Polygraph (Lie Detector)?
By Marvin Badler - Forensic Psychophysiologist
The word "polygraph" means "many things." The name refers to selected physiological activities are concurrently collected and recorded. The Polygraph instrument simultaneously records changes in physiological processes such as heartbeat, blood pressure, and respiration.

There are two basic types of polygraph instruments in use today. There is the analog instrument (the kind where you can see the pens moving over the chart paper) and the more advanced computerized polygraph instruments.

A polygraph instrument will collect physiological data from at least three systems in the human body. Convoluted rubber tubes placed over the examinee's upper chest and abdominal area will record respiratory activity. Two small metal plates attached to the fingers, will record electro-dermal (sweat gland) activity. A blood pressure cuff or similar device will record cardiovascular activity (blood pressure and pulse).

A polygraph examination will involve three phases. They are the pretest interview phase, the in-test phase and the post-test interview phase. A typical polygraph examination will last two to three hours, sometimes longer.

In the pretest phase, the polygraph examiner will complete required paperwork and talk with the examinee about the test. During this period, the examiner will discuss and review the questions to be asked, discuss the issue being tested on, and familiarize the examinee with the testing procedure and the polygraph instrument.

During the chart collection phase, the examiner will administer the polygraph examination and collect a number of polygraph charts. Following this, the examiner will analyze the charts and render an opinion as to the truthfulness of the person taking the test. The opinion rendered will be one of the following: No Deception Indicated (truthful), Deception Indicated (not truthful), Inconclusive (the examiner is unable to determine truthfulness or deception), or No Opinion (the examination had to be stopped before completion or some abnormality was noted).

In the post-test phase, the examiner will offer the examinee an opportunity to explain physiological responses in relation to one or more questions asked during the test.

Errors in Polygraph Examinations:
The False Positive & the False Negative
&bullWhile the polygraph technique is highly accurate, errors can occur. Polygraph errors may be caused by the examiner's failure to properly prepare the examinee for the examination or by a misinterpreting, the physiological data collected during the polygraph examination.

Errors usually are false positives or false negatives. A false positive occurs when examinees is truthful is reported as being deceptive. A false negative occurs when the examinee is deceptive is reported as truthful.

Since it is recognized that any error is damaging, examiners utilize a variety of procedures to identify the presence of factors, which may cause false responses, and to insure an unbiased review of the polygraph records.
Who Gets Results?
According to various state licensing laws and the American Polygraph Association's Standards and Principles of Practice, polygraph results can be released only to authorized persons. Generally, the individuals who can receive test results are the examinee and anyone specifically designated in writing by the examinee. Such as the person, firm, corporation or governmental agency, which requested the examination and others as, may be required by due process of law.
Admissibility in Court
It is largely the public's general opinion that polygraph testing results are not allowed in court.

The fact is that polygraph results are admissible in most courts across the country. The Supreme Court has yet to rule on the issue of admissibility so it has been up to individual jurisdictions to allow or disallow them.
Why is this public opinion so widespread? The simple fact is that both the plaintiff and the defendant have to agree on having the results of the test are admissible prior to the examination being conducted.

Since the results of the test are likely to benefit one party and not the other, the likelihood that both parties will agree to admissibility before knowing how it will affect their case is small. Because of this, results of polygraph testing are rarely admitted as evidence.

Information Source: The American Polygraph Association




These are just some areas in which the use of the polygraph has been proven beneficial.
&bullCriminal Defense
&bullIdentify the Guilty
&bullClear the Wrongfully Accused
&bullVerify Information & Statements
&bullViolent Crimes
&bullProperty Crimes
&bullSex Crimes & Allegations of Sexual Misconduct
&bullSexual Harassment
&bullNarcotic Investigations
&bullHidden Assets
&bullDomestic Disputes
&bullInfidelity Issues
&bullInsurance Fraud
&bullAllegations of Child Abuse
&bullCivil Rights Matters
&bullAllegations of Official Misconduct
&bullAllegations of Public Corruption
&bullEqual Employment Opportunity Matters
&bullWhite Collar Crimes
&bullMissing Persons
&bullLaw Enforcement, Government & Security Screening
&bullAny Time the Need for the Truth is Important

www.marvinbadler.com

Technology
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 

» More on Technology