Last month on our blog, we noted a story involving a Florida man's use of a polygraph test to try to clear himself from accusations of sexual misconduct. While the story helped to highlight the relatively limited situational use of the polygraph test, some readers may be left with questions about the accuracy of a polygraph in the criminal law context: is the test infallible? What happens if errors are made? To answer these questions, we'll turn to the American Polygraph Association, with the understanding that the information is intended to be general in nature only and not specific legal advice.
According to the American Polygraph Association, errors can occur during the test despite its relatively high degree of accuracy. An examiner may have failed to give the subject clear instructions or otherwise help him or her prepare as necessary for the test. The examiner may also fail to correctly interpret the data provided on the polygraph charts regarding the subject.
In the end, even if the examiner does everything right, the Association notes that a "false positive" or "false negative" may still occur. A false positive is when the test shows that an honest subject is being deceptive. A false negative is when the test fails to detect deception and reports that a lying subject is telling the truth.
So what can be done when a defendant facing a criminal charge takes a polygraph test and an error occurs? A criminal defense professional can help challenge the test results in court on a number of grounds. The examiner's credentials or licensure may be subject to scrutiny, as well as his or her formal training. If he or she asked the subject any inappropriate questions, the admissibility of the results may also be called into question.
Source: American Polygraph Association, "Frequently Asked Questions," accessed on Dec. 1, 2017