Why it Doesn’t Matter that Zimmerman Passed First Lie Detector Test

COMMENTARY | According to a story by USA Today, Florida prosecutors have released a confidential report showing that George Zimmerman passed a lie detector test the day after he shot Trayvon Martin. The test consisted of nine questions, with only two relating to the deadly incident. The Stanford, Fla., police report cited by USA Today shows that the test was given on Feb. 27 and the results of the test show that Zimmerman “told substantially the complete truth” in regards to this examination.

Zimmerman told police that Martin punched him in the nose, which knocked him to the ground. He said that Martin then repeatedly banged the back of his head into the pavement. Zimmerman also told police that Martin tried to get his gun from a holster on his waist and that was when Zimmerman shot the teenager. Zimmerman was eventually charged with second-degree murder, claiming that his actions were in self-defense.

The fact that Zimmerman passed the polygraph will likely have an effect on those following this case; however, it really should not. Polygraphs are usually not admissible in court because repeated studies have found the tests are unreliable. In 1998, the United States Supreme Court ruled that banning polygraph results in court was allowed, stating that “There is simply no consensus that polygraph evidence is reliable.

In 1994, psychologists at the University of Utah published a report outlining several ways that the accuracy of a polygraph could be affected, such as pushing your toes to the floor, biting your tongue, or counting backwards by sevens. A survey in 1997 of 421 psychologists found that the average validity of polygraphs is only about 61 percent.

While there have been several studies completed that show the validity rates as much higher — even as high as 98 percent — there is simply too much leeway in the results of a polygraph. This is especially true when there is a person’s future at stake in a criminal case or when prosecutors are trying to speak for a victim. Zimmerman might have passed that polygraph on the night he shot Martin; however, was the validity of the test that night at 61 percent or at 98 percent? There is simply no way to know for sure.