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There is a common perception that the polygraph has been removed from the American courtroom. Sadly, that perception is false. A quick Google news search yields a long list of recent unfortunate examples. In one story, a convicted child molester submits to periodic polygraph examination after release so that parents can feel more at ease. In another, a man is interrogated using a lie detector. One even shows that the results of a polygraph test can be used as evidence against you in a rape case. So what does American law really have to say about lie detectors? As with all legal questions that haven’t been directly addressed by the Supreme Court, the answer is “it depends,” and “it’s confusing as hell.” The relevant state and federal rules are a shifting patchwork of contradictory statutes and common law.
For example: Some states have declared the polygraph inadmissible in court regardless of the wishes of the defendant or prosecutor. 1 Other states allow polygraph results to be presented to a jury as evidence if both sides agree to let them in. 1 Massachusetts doesn’t allow polygraph evidence to be used in court but considers it useful in obtaining warrants. 1 No defendant or witness can be forced into taking a lie detector test. 1 Yet police investigations frequently use polygraphs to elicit confessions from suspects. 1 Admissibility in Federal Court is dependent on whether or not one can convince the judge polygraphs are “relevant and reliable“. (This is known as the “Daubert standard” of scientific evidence.) 2 The Employee Polygraph Protection Act of 1988 (EPPA) tightens the reins on most private employers who simultaneously engage in interstate commerce and polygraphy. It prohibits the screening of prospective employees and tells employers they my not coerce, discipline, or discharge their workers based on the results of any such test. 3 On the other hand, the EPPA does not apply when an employee is suspected of theft or to government employment opportunities. 3 In United States v. Scheffer, the Supreme Court held 8 to 1 (John Paul Stevens dissenting) that polygraph evidence may not be used in court martial proceedings because of its unreliability. They chose not to extend the ruling to all court battles. 4
Confused by the schizophrenia of these positions? That‘s a perfectly normal reaction. Legislatures and the courts are being wooed (no pun intended) by two hopeful suitors: the scientific community and the pseudoscientific community. Each have claimed their share of victories.
On the side of pseudoscience, they promise the moon5: According to the American Polygraph Association over 250 studies have been conducted on the accuracy of polygraph testing during the past 25 years. Recent research reveals that the accuracy of the new computerized polygraph stytem [sic] is close to 100%.
The The Office of Technology Assessment (R.I.P. 1975-1995), the official science advisors to Congress, disagreed:
The wide variability of results from both prior research reviews and OTA’S own review of individual studies makes it impossible to determine a specific overall quantitative measure of polygraph validity. These opinions are echoed by the National Academy of Sciences: […] the NAS extrapolated that if the test were sensitive enough to detect 80% of spies (a level of accuracy which it did not assume), this would hardly be sufficient anyway. Let us take for example a hypothetical polygraph screening of a body of 10,000 employees among which are 10 spies. With an 80% success rate, the polygraph test would show that 8 spies and 1,992 non-spies fail the test. Thus, roughly 99.6 percent of positives (those failing the test) would be false positives. Keep in mind that real spies are also the people with the most interest in researching and using countermeasures to avoid detection. The OTA and NRC are joined by The Journal of Forensic Psychology Practice, The Journal of Applied Psychology, The American Psychological Association, and many others. They all agree that polygraphy is poorly structured, hard to standardize, subjective, vulnerable to countermeasures, and heavily biased. In retrospect, this is an obvious conclusion. Red flags should go up whenever your biggest supporter is Maury Povich.
Footnotes:
1. State Admissibility of polygraph evidence
2. Daubert v. Merrell Dow Pharmaceuticals
3. The Employee Polygraph Protection Act of 1988
4. United States v. Scheffer
5. www.truthorlie.com
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It is possible one could cut down on the number of false positives by using as indicators only questions that would only have significance to a guilty party, about which only the guilty party could have any knowledge.
This is probably not very practical however.