Police, Feds Use Popular Polygraph Device That Makes Critical Errors


Police departments and federal agencies across the U.S. use a type of polygraph despite evidence of a technical problem that could label truthful people as liars or the guilty as innocent, McClatchy Newspapers have found. As a result, innocent people might have been labeled criminal suspects, faced greater scrutiny while on probation, or lost out on jobs. Just as alarming, spies and criminals may have escaped detection. The technical glitch produced errors in the computerized measurements of sweat in one of the most popular polygraphs, the LX4000. Polygraphers first noticed the problem a decade ago, but many government agencies hadn't known about the risk of inaccurate measurements until McClatchy raised questions about it.

The manufacturer, Lafayette Instrument Co. Inc., described the phenomenon as “occasional” and “minor,” but it couldn't say exactly how often it occurs. Even after one federal agency became concerned and stopped using the measurement and a veteran polygrapher at another witnessed it repeatedly change test results, the extent and the source of the problem weren't independently studied nor openly debated. In the meantime, tens of thousands of Americans were polygraphed on the LX4000. The controversy casts new doubt on the reliability and usefulness of polygraphs, which are popularly known as lie detectors and whose tests are banned for use as evidence by most U.S. courts.

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