Question

A polygraph (lie detector) is an instrument used to determine if an individual is telling the truth. These tests are considered to be 96% reliable. In other words, if an individual lies, there is a 0.96 probability that the test will detect a lie. Let there also be a 0.008 probability that the test erroneously detects a lie even when the individual is actually telling the truth. Consider the null hypothesis, "the individual is telling the truth," to answer the following questions.

a. What is the probability of a Type I error? (Round your answer to 3 decimal places.)
  

b. What is the probability of a Type II error? (Round your answer to 2 decimal places.)
  

Answer 1

a. P(Type I error) = P(test erroneously detects a lie even when the individual is actually telling the truth) = 0.008

b. P(Type II error) = P(test erroneously detects a truth even when the individual is actually telling the lie) = 1-0.96 = 0.04