88 Polygraphs & Lies

What’s The Truth About Lie Detectors?  Courts, including the United States Supreme Court (cf. U.S. v. Scheffer, 1998 in which Dr. Leonard Saxe’s research on polygraph fallibility was cited), have repeatedly rejected the use of polygraph evidence because of its inherent unreliability. A “lie detector” only infers deception by analyzing physiological responses to an unstandardized series of questions.

The polygraph typically records three indicators of arousal: heart rate/blood pressure, respiration, and skin conductivity. The procedure compares responses to “relevant” questions (e.g., “Did you shoot your wife?”), with “control” questions concerning misdeeds that are similar to those being investigated, but refer to the person’s past, e.g., “Have you ever betrayed someone who trusted you?”

People are assumed to fear control questions designed to arouse their concern about their past truthfulness, more than relevant questions asking about a crime they know they did not commit.  Thus, persons are labeled “deceiving” if they respond more to relevant questions.  Yet, there is no evidence that any pattern of physiological reactions is unique to deception. An honest person may be nervous when answering truthfully and a dishonest person may not be anxious.

Most psychologists agree there are few good studies showing that polygraph tests can accurately detect lies. Remain skeptical about any conclusion wrung from a polygraph.