Are the results of lie detector tests admissible in court?

“Liar, liar… pants on fire!” Children all over the English speaking world know this sing-song rhyme. It is “sung” when someone gets busted telling a lie. Police investigators have used lie detectors, also known as “polygraphs,” for over a century now. The first polygraph was invented in 1921, when a California police investigator and physiologist, John Larson, created a machine that simultaneously measured changes in blood pressure, heart rates, and respiration rates to assist in the detection of deception (Larson, Haney, & Keeler, 1932; McCormick, 1927).

After over a hundred years of its invention, one might think that polygraph test results would be admissible court evidence.

However, “[p]olygraph results are inadmissible in Florida because of their inherent unreliability; or put another way, because their reliability has not been scientifically demonstrated to a degree of certainty with which the courts are comfortable.” See Davis v. State, 516 So.2d 953, 955 (Fla. 4th DCA 1986); see also Griffin v. State, 958 So. 2d 1000, 1001 (Fla. 1st DCA 2007) (“The results of a polygraph test remain inadmissible in both civil and criminal cases because of unreliability. Lane v. State, 762 So. 2d 560, 561 (Fla. 5th DCA 2000) (citing Farmer v. City of Ft. Lauderdale, 427 So. 2d 187 (Fla.1983)”); Lieberman v. Department of Professional Bd. of Medicine, 573 So.2d 349, 351-352 (Fla. 5th DCA 1990) (“It is and has been the rule in Florida that polygraph results are inadmissible as evidence.”) (citing cases).

The Florida Supreme Court approved of the opinion in Davis. See Davis v. State, 520 So.2d 572 (Fla 1988).

In the rare cases where parties agree to admit polygraph test results, the jury must be instructed as to the strengths and weaknesses of such evidence, as to what the test results are calculated to determine, and that it is for the jury to determine what weight should be given to such evidence.

Id. at 574 (Florida Supreme Court announcing rule that agreements to the admissibility of polygraph results must be in writing and signed by the parties). Whether Artificial Intelligence will play a role in making polygraphs more reliable remains to be seen.