The Pitfalls of the Lie Detector Part 1

Before anyone jumps on my case, I know that there is no “lie detector” but only a polygraph.  I understand the basics of how it works and the nature of the questions.  What this post is about is the idea that there are basic pitfalls in putting emphasis on the polygraph.

Pitfall #1:  Using the polygraph for pre-employment screening.  The reason this is a pitfall, is that this is actually the worst possible use of a polygraph.  The National Academy of Science studied the use of polygraph examination to determine if they were effective on screening security risks.  They found of course that they are not.   Specifically, they said “Basic science and polygraph research give reason for concern that polygraph test accuracy may be degraded by countermeasures, particularly when used by major security threats who have a strong incentive and sufficient resources to use them effectively. If these measures are effective, they could seriously undermine any value of polygraph security screening.” The real and important question to ask then is why does the government rely heavily, almost exclusively on the polygraph for security clearance?

What the National Academy of Sciences found was this: “There has been no serious effort in the U.S. government to develop the scientific basis for the psychophysiological detection of deception by any technique, even though criticisms of the scientific grounding of polygraph testing have been raised prominently for decades. Given the heavy reliance of government on the polygraph, especially for screening for espionage and sabotage, the lack of a serious investment in such research is striking.”

Now polygraph practitioners, or “examiners” will staunchly claim the validity and veracity of polygraph examinations.  Of course they do, this is their bread and butter.  Anyone that can be swayed by their arguments in reality is actually just gullible.  The whole essence of the use of polygraphs is the mystique that surrounds them.  Examiners and practitioners keep the way they operate the polygraph a closely held secret – supposedly so that people cannot learn to “beat” the polygraph.  As a matter of fact, if the examiner even merely suspects that the person being examined is using or attempting to use counter-measures – they are automatically assumed to be showing deceptive behavior.

The pre employment screening examination has to make the following assumption: that a person who is deceptive about certain undesirable past acts is at risk for committing different kinds of undesirable acts in the future.  First of all, there is absolutely no empirical scientific evidence that this indeed is true.  Secondly,  the examiner always can be totally subjective in their conclusion that the subject was deceptive.

There is a  simple fact that the “accuracy” of a particular examination depends upon the purpose of the test. This makes it unwise to assume that “accuracy” estimates calculated from data when the polygraph is used for a specific purpose, such as finding a perpetrator of a particular crime, can be in even the remotest way be applied to its use for pre-employment screening.  I put the accuracy in quotes, as whenever an examination takes place, and the examiner tells the subject that (s)he thinks the subject is deceptive on something, and then gets a “confession” the test is considered accurate and a success.  It does not matter if the confession was even true, real, or accurate.

Most of these tests are based on the principle of the “Control Question Test” or CQT. As you may or may not know, for the CQT to be valid, you first have to make two assumptions. If you are seeing the pitfall already, good for you. The first of these two assumptions requires that people who are innocent are more responsive to control questions than they are to relevant questions. The second assumption that is made is that guilty persons will respond more intensely to relevant questions than they do to the control questions. The fact that both of these assumptions are not necessarily true can be easily challenged.

By the time I end this series on lie detector tests, you will probably know more than you ever wanted to know about polygraph tests.

Whatever you do - stay safe!