Are Polygraph Tests Reliable?

It seems like in every television show depicting law enforcement and the criminal trial process, a suspect is hooked up to a polygraph, or lie detector machine, and made to answer questions about a crime they are accused of being involved in. The purpose of these machines is to record the stress that manifests when someone is being asked particularly challenging questions and record how a person's natural and internal body processes react to these stressors.

How does the machine test if someone is lying?

Lie detector tests measure breathing rates, pulse, and galvanic skin response and print out the results on graph paper. The graph paper shows when any natural biological response corresponds with questioning. If it reads that someone's breathing quickened, their pulse raced, or the level of sweat on the skin increased, it indicates that the person being questioned was stressed, and may be lying.

There are some reasons why polygraph tests are used during questioning:

• Very few people are able to control all of their biological stress responses at the same time
• Pre-examination tests are run on a suspect to allow the questioner to measure their reactions to telling a lie

The pre-examination tests work to determine a subject's level of stress at being questioned to begin with. Neutral and intentionally emotional questions will be asked to initially determine stress responses. When the important questioning begins, the responses that are given are compared to the control questions and used to determine what answers may include a lie.

But does this mean that polygraph tests are reliable? In many cases the courts doubt the reliability of polygraph tests since many people can conceal stress, generate their own artificial stress, and even disassociate themselves from the truth. Not only that, there is no way to differentiate whether the stress is caused by the test in general or the result of a particular lie. If lie detector tests were still considered so reliable, they would be used more often in court cases when questioning important witnesses.

If you are concerned about the role that a lie detector test may take in an upcoming questioning, contact an Illinois criminal defense attorney. The Law Office of Michael P. Schmiege offers free, confidential consultations to begin your defense against criminal charges.