Polygraph test error rates. In a classic study reported in Discover magazine, a group of physicians subjected the polygraph (or lie detector) to the same careful testing given to medical diagnostic tests. They found that if 1,000 people were subjected to the polygraph and 500 told the truth and 500 lied, the polygraph would indicate that approximately 185 of the truth tellers were liars and that approximately 120 of the liars were truth tellers.

a. In the application of a polygraph test, an individual is presumed to be a truth teller 1H02 until “proven”

a liar 1Ha2. In this context, what is a Type I error? A Type II error?

b. According to the study, what is the probability (approximately)

that a polygraph test will result in a Type I error?

A Type II error?