This type of test is based on the premise that muscles in the voice box tighten or loosen, which changes the sound of the voice. The small, involuntary frequency modulations in the voice when under stress (i.e., lying) are measured. Studies show that this type of tests operates at about a chance level or slightly higher (50-65% accurate). That means it would be similar to a flip of a coin. Source: Journal of Forensic Sciences, 53(1), 183-193, Hollien and Harnsberger (2008)
