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 licd, the polygraph would indicate that approximately 185 of the truth-tellers were liars and that approximately 120 of the liars were truth-tellers

(Discover, 1986).

a. In the application of a polygraph test, an individual is presumed to be a truth-teller (H,)) until "proven" a liar (H,). In this context, what is a Type I error? A Type I1 error'?

b. According to the study, what is the probability (approximately) that a polygraph test will result in a Type I error? A Type I1 error?