WASHINGTON — Police departments and federal agencies nationwide are using a type of polygraph despite evidence of a technical problem that could label truthful people as liars or the guilty as innocent, McClatchy has found.As a result, innocent people might have been labeled criminal suspects, faced greater scrutiny while on probation or lost out on jobs. Or, 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. Although polygraphers first noticed the problem a decade ago, many government agencies hadn’t known about the risk of inaccurate measurements until McClatchy recently raised questions about it.The manufacturer, Lafayette Instrument Co., 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 saw it repeatedly change test results, the extent and the source of the problem weren’t independently studied or 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. Scientists have long questioned whether polygraphers can accurately identify liars by interpreting measurements of blood pressure, sweat activity and respiration. But polygraphers themselves say they rely on the measurements to be accurate for their daily high-stakes decisions about people’s lives.“We’re talking about using a procedure that has a very weak scientific foundation and making it worse,” said William Iacono, a University of Minnesota psychology professor who’s researched polygraph testing. “I already don’t have very much confidence in how government agencies conduct these tests. Now, they might as well be flipping a coin.”Despite the scientific skepticism, intelligence and law enforcement agencies see the polygraph as useful in obtaining confessions to wrongdoing that wouldn’t otherwise be uncovered. Fifteen federal agencies and many police departments nationwide rely on polygraph testing to help make hiring or firing decisions. Sex offenders and other felons often undergo testing to comply with probation or court-ordered psychological treatment. Police detectives and prosecutors rule out criminal suspects who pass and scrutinize those who don’t.The Texas Department of Criminal Justice uses polygraph testing for sex offenders released on supervision as a part of their treatment program. The department employs four polygraph contractors, which use Lafayette instruments, as well as some made by a firm called Axciton.In its ongoing series about polygraph use by government agencies, McClatchy found that such testing has flourished despite being banned for use by most private employers 25 years ago. For federal jobs alone, more than 70,000 people are polygraphed each year, and most can’t challenge the results in court or allege abusive tactics. While supporters say accuracy can be 85 to 95 percent, polygraphs aren’t required to meet any independent testing standards to verify the accuracy of their measurements, unlike medical or other computerized equipment.The concerns about the LX4000 only add to the criticism.“If you buy all of the propositions that the physiological measurements are a reliable proxy for truth telling or deception, then the whole premise depends upon a machine that can precisely record those measurements,” said Gene Iredale, a San Diego attorney. “If you don’t have that, then you have a hope piled on a speculation, and on top of it all an error-filled system.”In the absence of an independent assessment, polygraphers depend on the federal government, the manufacturer or one another to be notified of a problem with the technology. Many polygraphers, however, told McClatchy they didn’t know about the possibility of inaccurate measurements or that they could occur in other polygraphs that use the same technology.“If this was being debated, I would have liked to have known about it,” said Danny Fields, the supervisor of the Kansas City Missouri Police Department’s polygraph section, which used the LX4000 for years before replacing it with a newer Lafayette model. “I believe in polygraph 100 percent, but I want to make sure it’s working like it’s supposed to be working.”The polygraph profession is highly secretive, and many agencies say national security or law enforcement interests bar them from answering questions. Of 63 federal, local and state agencies contacted by McClatchy, only 40 would say what types of machines they used.Of those, 27 state and local agencies said they either currently use or have used the LX4000, including big-city police departments such as New York, Chicago and Los Angeles. None of those agencies said they were reviewing their previous tests for errors, although some people who’d failed polygraph tests said they thought they’d been inaccurately labeled. Ten federal agencies have used Lafayette polygraphs.“I’m astounded that a government agency would rely on this machine to make any decision,” said John Stauffer, a Chicago accountant who was denied an FBI job in 2011 because he didn’t pass his polygraph test. “I’ve always known that I shouldn’t have failed. Now I wonder whether this was the problem.”Measuring sweatScientists have experimented for more than a century with running a tiny amount of electricity through sweat glands in the fingertips as a way to gauge emotions and mental effort. In the past two decades, however, polygraphs marketed to government agencies have changed the way perspiration is measured.As a result, the LX4000 measures sweat in two ways. One method, known as the manual mode, directly measures the secretions from sweat glands, as scientists have traditionally done. The other, known as the automatic mode, electronically filters the measurements and is designed to smooth out the sometimes erratic graphic representations and make them easier to interpret.David Reisinger, a veteran federal polygrapher, said he first saw a problem with the LX4000 in 2005, while discussing a test with a Lafayette employee by phone. When he switched between the two modes, he noticed a difference in the measurements.“It was so significant I noticed the problem immediately,” said Reisinger, a polygrapher at the Defense Intelligence Agency at the time. “It jumped right off the screen at me.”Reisinger pressed the company to look into it because he saw it could change the outcome of a test depending on the setting. Polygraphers assign numbers to sweat measurements and add them up for a final score that’s supposed to show whether someone is lying. In a test where one point can make a difference, Reisinger documented up to a 16-point difference between the two modes.He notified his supervisors, and Lafayette pledged to fix it.Waiting for a fixYears and dozens of examples later, the company still hadn’t, he said.“What troubled me is that they couldn’t tell me which measurement was accurate,” he said.The Air Force’s Office of Special Investigations noticed a problem as early as 2002, the year the LX4000 hit the market. A spokeswoman said her law enforcement agency was concerned that it could change the outcome of tests and sought out Lafayette officials.“They recommended that all polygraph charts be collected in the manual mode,” spokeswoman Linda Card said in a statement. “As a result of the possible flaw in the automatic mode, we, as an organization, directed the use of only the manual mode” during testing.The manufacturer’s advice apparently didn’t reach other government agencies.“This is news to me,” Reisinger said. “The manufacturer never told us that.”Instead, Lafayette described the problem to the Defense Intelligence Agency as “minor” and repairable. In one email, then-Lafayette Operations Manager Mark Lane told the agency in 2007 that company officials felt “extremely confident” they could fix it, adding that they had “devoted our entire engineering efforts” to fixing the automatic mode.“We certainly agree that this is an issue that needs to be resolved,” he told DIA officials.