Predictive power of the polygraph: can the "lie detector" really detect liars?

Expanded use of the polygraph as a detector of lies has been proposed in the United States and the United Kingdom. The positive predictive value of the polygraph (ie, the proportion of positive test results that are true positives) was assessed, on the evidence of the best published data for the sensitivity and specificity of the device. In many screening or investigative situations, the predictive value would be poor; most of the positive results would be false positives. Consequently, truthful persons incriminated as liars by the polygraph would outnumber actual liars with a positive result on the test.