SUBTEXTdepend heavily on the polygraph to keep from hiring the wrong
kind of employees.
The great majority of polygraph tests, about 300,000 a year
are given by businesses as part of pre-employment screening to
control internal crime and to recommend promotions. In thirty-
one states, it is legal to require employees to take a polygraph
test. In only eighteen states is it illegal, and even in those states
employers can usually find a way around the law. An Office of
Technology Assessment report states that to get around the law,
employers may tell a worker they suspect him or her of theft,
but if innocence can be demonstrated in a polygraph test, the
employer will not discharge the employee.
Banks and drugstores, convenience stores, groceries, and fast-
food outlets rely heavily on polygraph testing for pre-employment
screening. The Justice Department, the FBI, and most police de-
partments use the polygraph after investigators have narrowed down
a list of suspects. Many government agencies count on the polygraph
for lie detection.
The sad part of all this is that the polygraph is not a lie detector.
All it can do is detect changes in our autonomic nervous system:
changes in heart rate, blood pressure, skin conductivity, tempera-
ture, breathing, sweating, flushing, and blanching—all physical
responses that have been linked to emotional arousal.
The theory behind the polygraph is that when we tell a lie, we
show a certain amount of emotional arousal. This arousal can be
charted by the machine, and the operator can pinpoint which
questions caused it—and thus, theoretically, which of the subject's
responses are lies.
Unfortunately, there are many problems associated with this
technique. The greatest one is that most people can be emotionally
aroused by things besides lying. If the question asked by the