What is a polygraph?

The word "polygraph" literally means "many writings". The name refers to the manner in which selected physiological activities are simultaneously recorded. What we today refer to as a polygraph or lie detector is a scientific instrument, which is capable of simultaneously recording two or more channels of data. This data is the specific physiological changes produced by an individual when he/she is asked questions pertaining to a specific area under investigation. These recordings or graphs which are known as "polygrams" are then interpreted by a polygraph examiner.

How accurate is a polygraph?

Recent research reveals that the accuracy of the new computerized polygraph system is close to 100%. In the past 75 years, over 250 studies have been conducted on the validity, accuracy and reliability of polygraph testing (American Polygraph Association 1996 Polygraph Issues & Answers). Based on twelve separate studies involving 2,174 real cases since 1980, evidence suggests that qualified field polygraph examiners are 98% accurate in their overall decisions (Ansley, N. 1990 The validity and reliability of polygraph decisions in real cases).

How long does it take to conduct a polygraph test?

Depending on the complexity of the case and the issues being tested a polygraph test usually takes between 30-40 minutes (demonstration tests) to 2-3 hours.

What happens during a polygraph test?

A polygraph test consists of three phases: 1) pretest interview, 2) chart collection and 3) chart analysis and post-test interview.

>Pretest Interview
The average polygraph test lasts 2-3 hours. The longest part of the examination will be the 45-90 minute "pretest interview". During the pretest interview the examiner covers such topics as:
a) explanation of the subject’s legal rights,
b) complete explanation of the polygraph and its components,
c) complete explanation of how the polygraph works, d) review of case facts and issues,
e) review of all questions to be asked during the actual polygraph examination,
f) provide detailed instructions for the actual testing phase and
g) confirm the examinee’s understanding of these topics.

>Chart Collection
During the chart collection phase the examiner attaches the required sensors to the examinee. This procedure is totally painless. In order to reduce distractions for the examinee, polygraph exams are conducted in private with no other persons permitted in the examination room (other than an interpreter, if required).

After the sensors are attached to the examinee the recording process commences. The polygraph examination consists of asking the subject a set of previously reviewed questions and recording on a digital polygraph recorder the subject’s physiological responses to the questions. Questions are read to the examinee several times during the recording process. Typically two or three charts are recorded. After each question is asked, a 25 second period follows whereby the instrumentation records autonomic responses to each question. The examinee is given a rest period of at least 5 minutes between each chart recording.

>Chart Analysis and Post-test Interview

After the collection of charts is concluded the polygrams are scored by computer using scoring algorithms. The charts are also numerically scored by the examiner, who then renders his opinion. If further questions exist after the scoring is concluded, the examiner will seek a second opinion.

Do nerves affect the results of a polygraph test?

No. It is expected that all people who undergo a polygraph test will be nervous whether they intend to answer questions truthfully or not. An examiner will look for action specific responses over and above the examinee's heightened level of nervousness or anxiety. Typically an examinee remains nervous throughout the entire testing process not at one individual question. If nerves affected the result of a polygraph test, then nobody would ever pass a test.

Can you beat the polygraph examination?

No, you can’t. If the examinee knows he/she is lying, the polygraph will detect the lie. Any experienced polygraph examiner can detect deception.

Polygraph has a very high accuracy rate of almost 97 percent, and a qualified examiner is trained to pick up techniques that an examinee may use in order to "fool" the instrument. People do not beat a polygraph test; they beat the examiner conducting the test. This is why it is imperative to ensure that the examiner conducting the test is qualified.

A polygraph is simply an instrument that records changes in autonomic reactivity when confronting a given stimulus (question). If a person engages in behaviors that are designed to distort the polygraph tracings, then it is the job of a competent and qualified examiner to identify and determine when this is occurring.

In most cases it is easy for a qualified examiner to determine when an examinee is attempting to influence the outcome of the exam. Although some parameters can be consciously controlled these are usually easily detected.

What should I look for when seeking a polygraph examiner?

It is important that you choose a polygraph examiner who has been professionally trained.

After training, each qualified examiner must serve an "internship" whereby their work is quality controlled and evaluated to ensure that the appropriate testing formats are used and that questions are properly formulated according to current testing methodology.

It is also important to ensure that the examiner regularly undertakes training and attends seminars relating to continuing education that deals with changes in technology, methodology and practices. Additionally, it is beneficial to look for a polygraph examiner who has professional affiliations and memberships with recognized associations and/or organizations that set professional standards for its members. Ensure that your examiner fulfils each of the above requirements.

There are some unethical people, who have represented themselves as qualified polygraph examiners when in fact they have no formal training or qualifications. Often unqualified polygraph examiners will charge substantially less than a qualified examiner, who has undergone extensive training. Using an unqualified polygraph examiner may be cheaper, but is dangerous and will produce false results.