Polygraph Questions And Answers With Legal Pub

Reader: Legal Pub, You have tried many jury trials. How is it that you have developed a knack for deciding whether a witness is telling the truth?

Legal Pub: First, thanks for the question. Second, contrary to popular belief, lawyers do not always know whether a witness is telling the truth unless they have impeachment evidence available for contradiction. Impeachment evidence in the form of prior statements or physical evidence is demonstrative evidence of fabrication. Without such concrete evidence, the discussion turns to nonverbal communication which is not always reliable.

The first nonverbal signs often discussed in criminal cases is polygraphs. Unfortunately, the polygraph is not as reliable as many people think. The so called lie detector test measures nonverbal signals such as increased perspiration, increased heart rate, blood pressure, changes in respiration, voice inflection, and/or skin conductivity to identify signs consistent with fabrication. Some polygraphs now measure changes in the pupil thought to correspond with not telling the truth. Other non verbal signs include failure of the witness to look the cross examiner in the eyes. Pupil dilation may also give a clue to the veracity of ones statement. However, like a polygraph, the reliability of such findings is questionable.

Reader: How reliable are polygraphs?

Legal Pub: In my view, they are not reliable and a client should not submit to a lie detector test even if he is innocent because scientific data calls into question the reliability of polygraphs. ("Scientific Validity of Polygraph Testing: A Research Review and Evaluation". Washington, D. C.: U.S. Congress Office of Technology Assessment (1983). ) Advocates may argue that the test is 90% - 95% reliable, but too often the polygraph is just a means to launch an aggressive interrogation. In 1997, 421 psychologists concluded that the accuracy of polygraphs is about 61%. (USA Today LINK).

Our Supreme Court in United States v. Scheffer, concluded: “There is simply no consensus that polygraph evidence is reliable” and “Unlike other expert witnesses who testify about factual matters outside the jurors' knowledge, such as the analysis of fingerprints, ballistics, or DNA found at a crime scene, a polygraph expert can supply the jury only with another opinion...”. An Also, in 2005 the 11th Circuit Court of Appeals stated that “polygraphy did not enjoy general acceptance from the scientific community."United States v. Henderson (May 23 2005).

False positives on innocent people remains a genuine concern. .William G. Iacono, from the University of Minnesota, published a paper titled “Forensic “Lie Detection": Procedures Without Scientific Basis” which concludes that polygraphs may be useful as a tool to induce confessions; however, it not a scientifically credible test.

Polygraph testimony can be admitted by stipulation in many states. Daubert v. Merrell Dow Pharmaceuticals (1993) provides the standard for admitting such evidence if the "underlying reasoning or methodology is scientifically valid and properly can be applied to the facts at issue." Currently no state can force a defendant or witness to undergo a polygraph. In Massachusetts, Maryland, New Jersey, Delaware and Iowa an employer may not require a polygraph either as conditions to gain employment or as a condition to remain employed. The Employee Polygraph Protection Act of 1988 (EPPA) is generally in accord.

Reader: So what is a lawyer to do?

Legal Pub: Ultimately, the real finder of truth is a jury or judge.