The LX4000 measures sweat in two ways. One method, known as the manual mode, directly measures the secretions from sweat glands, as scientists traditionally have 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.Another fine classification scheme: random results.
David Reisinger, a veteran federal polygrapher, said he first witnessed 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.
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. Years 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.
Tuesday, May 21, 2013
Where Medical and Legal Theater Meet
Glitch in widely used polygraph can skew results
