U.S. Government studies have concluded that the single-issue (one
question) polygraph exam, conducted properly by a qualified examiner, is 87 to
95 percent accurate. It is the most accurate tool available today for determining
truth or deception. Accuracy of the multi-question exam drops to around
80 percent due to a number of psychological factors. These statistics do
not include "inconclusive" results in which no opinion can be made from
the polygraph charts, which happens about 20% of the time.
For more information click here: Validity
and Realiability of Polygraph Testing .