Question

A polygraph (lie detector) is an instrument used to determine if the individual is telling the truth. These tests are considered to be 86% reliable. In other words, if an individual lies, there is a 0.86 probability that the test will detect a lie. Let there also be a 0.070 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 Type I error? (Round your answer to 3 decimal places.)


Probability


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


Probability

Answer 1

Explanation:

a) The probability of a Type I error in a lie detection test would be the probability that the lie detection machine incorrectly detected lie for the truth tellers. This is already given in the problem as 0.07.

Therefore,

`P(Type-I) = 0.07`

Therefore 0.07 is the required probability here.

b) The probability of a Type II error in a lie detection test would be the probability that the lie detection machine incorrectly detected truth for the the people who are actually liars. This is thus 1 - reliability.

`P(Type-II) = 1 - Reliability = 1- 0.86 = 0.14`

Therefore 0.14 is the required probability here.

Answer 2

a) 0.070

b) 0.14

Explanation:

Given that the tests are 86% reliable, i.e a probability of 0.86 a lie would be detected.

Probability of error = 0.070

a) For type I error, we have:

The probability of a type I error in this lie detector is the probability that the test erroneously detects a lie even when the individual is actually telling the truth, i.e

P(type I error) = P(rejecting true null)

= 0.070

b) The probability of a Type II error this lie detectot is the probability that the test erroneously detected truth insteax of lie.

i.e = 1 - reliability

P (Type II error) = P(Failing to reject false Null)

= P(Not detecting a lie)

= 1-0.86

= 0.14