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Are Lie Detector Tests Reliable?


The Truth Behind the Lie (Detector)

Two people sit in a room. One person is attached to wires connected to a machine that contains a needle, while the other person interrogates them with straightforward questions. The needle moves up and down according to the person’s responses to the questions.

Sound familiar? This is how polygraph tests are portrayed in movies, and it’s similar to what you would expect in reality. This can be a nerve-wracking experience for people who aren’t familiar with the process, and since it’s uncommon to take a lie detector test, it’s fair to say that many people aren’t familiar with this experience.

You have the right to refuse a polygraph test, but if you consent to participate in one, you may accidentally self-incriminate yourself. Polygraph tests aren’t reliable for several reasons.

Problems with Polygraph Tests

A polygraph test is a type of lie detector test that measures your physiological responses to certain questions. According to the American Psychological Association (APA), a polygraph test measures three indicators of autonomic arousal: Heart rate/blood pressure, respiration, and skin conductivity. In criminal investigations, there are two common test formats: The Control Question Test (CQT) and Guilty Knowledge Test (GKT).

The CQT, the most common test format, examines the subject’s answers to questions that are relevant to the specific crime (i.e. Did you rob the bank?) The examiner will also ask similar questions that are not related to the crime (i.e. Have you ever obtained money outside of your employment?), and then compare both responses.

The GKT involves a multiple-choice test that only a guilty subject could answer. Referencing the prior bank robbery example, a GKT would involve questions like “Was $1,000, $1,500 or $2,500 stolen?” The APA describes that a GKT produces a “larger psychological reaction” to the correct answer choice, which can indicate deception. Unlike a CQT, a GKT requires investigators to have enough information about the crime to ask crime-specific questions in a multiple-choice format.

In both these tests, including other types of polygraph tests, there is plenty of room for error:

  1. Physiological reactions do not equal deception
  2. The subject must believe in the accuracy of the polygraph test to be fearful of being caught for lying, which makes them likely to answer truthfully
  3. External factors could affect the polygraph readings, such as nervousness, the testing environment and the examiner’s techniques
  4. The lie detector test can be tricked; subjects can “train” and “convince” themselves to believe their innocence so strongly that even the polygraph test can’t detect the real truth.

Our Santa Barbara criminal defense lawyers strongly advise that you do not consent to a lie detector test of any kind without consulting with an attorney first. Police officers may convince you that you need to take the test “or else,” but those are simply scare tactics: Just say no or explain that you want to speak to an attorney first.

Don’t be fooled by the lie detector test: It’s not 100% reliable. To learn more, please contact us at (805) 467-6060 today!

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