Polygraph Examination

Note: This explanation of how a polygraph examination is done starts on the page, Polygraph Testing 101.

As you answer the questions, the machine measures your physiological responses to determine if you are lying. However, there is much more to the test that the examiners don't tell you about.

There are actually three types of questions asked during a polygraph test (this is true for the " CQT" or "Control Question Test," the most common type in criminal matters). They are the "Irrelevant Questions," the "Control Questions," and the "Relevant Questions."

The irrelevant questions are ones to which the operator and you know the truthful answers. These may be questions like, "Is there a window in this room?" or "Is your name Mary?"

The control questions are also supposed to be questions that the tester knows the answers to. In reality, they are often questions to which the operator assumes he knows the truthful answer to, like "Have you ever stolen anything -- as a child or as an adult?" He assumes you have -- that all people have.

The control questions are supposed to make you uncomfortable -- whether you tell the truth or not. That discomfort gives the examiner a measurement of your response with which to compare your responses to the relevant questions. Lie or tell the truth, and you will likely still feel uneasy answering a question like;

Have you ever lied to a good friend -- even a small 'white lie'?

The examiner will say that you should answer all questions honestly, but he doesn't actually want this to happen. In fact, sometimes these control questions are called "probable lie control questions," because it is assumed you will answer with a lie. After a question like, "Have you ever lied when in trouble?" the tester may mention that someone who would do such a thing is suspect, thus encouraging you to lie, so he can see your response.

Examiners use this kind of trickery as a standard part of a polygraph examination. They also use their own judgment. How different does the response to a relevant question have to be from a control question to qualify as "deceptive?" Despite any training or rules, this is a judgment call (whether or not you think you can trust a machine, consider whether you can trust the judgment of a operator with limited training).

If the examiner thinks you are dishonest, he may interpret the results differently. Even if he doesn't do this, he may push harder to find questions that give the result he wants. Whether this is conscious or not, it shows how unscientific the whole procedure can be.

It is important to note that the whole polygraph examination does not consist just of the testing while the subject is connected to the machine. It starts the moment the subject enters the room and includes the following:

1. Observation of subject. Sometimes the subject will be watched through a two-way mirror or with hidden cameras.

2. The pre-test interview. This is when the process is explained to the subject, and the fear of dishonest responses is induced, as well as the belief in the process itself.

3. The "acquaintance test." Also called the "stim" test, this requires the subject to purposely lie while connected to the machine, so the tester can impress the subject by "detecting" that lie.

4. The test. The subject is questioned, and the responses recorded by the polygraph machine.

5. The post-polygraph examination interview. This may be the most important part of the test. It gives the tester an opportunity to obtain damaging admissions. For example, the tester may ask why the subject had a strong reaction to certain questions, to induce the subject to explain himself. He may ask if the subject wants to change any of his answers or explain more. This is essentially an interrogation, and the test itself is a tool of intimidation.

Continues here... How a Polygraph Works

Beat a Lie Detector Test | Polygraph Examination